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(PDF) Sex-specific costs of rearing a nestling and its implications in the brood sex ratio of Magellanic penguins | Javier Ciancio - Academia.edu
<!DOCTYPE html> <html > <head> <meta charset="utf-8"> <meta rel="search" type="application/opensearchdescription+xml" href="/open_search.xml" title="Academia.edu"> <meta content="width=device-width, initial-scale=1" name="viewport"> <meta name="google-site-verification" content="bKJMBZA7E43xhDOopFZkssMMkBRjvYERV-NaN4R6mrs"> <meta name="csrf-param" content="authenticity_token" /> <meta name="csrf-token" content="wdhRyxEOe5Z1CWqzlNIJgX++riNgwolVElKkroL59yqVNaox4VmTRTnDB4S4nkWQfD6l1CVFQ73nYQOqYsWjmA==" /> <meta name="citation_title" content="Sex-specific costs of rearing a nestling and its implications in the brood sex ratio of Magellanic penguins" /> <meta name="citation_author" content="Javier Ciancio" /> <meta name="twitter:card" content="summary" /> <meta name="twitter:url" content="https://www.academia.edu/91287099/Sex_specific_costs_of_rearing_a_nestling_and_its_implications_in_the_brood_sex_ratio_of_Magellanic_penguins" /> <meta name="twitter:title" content="Sex-specific costs of rearing a nestling and its implications in the brood sex ratio of Magellanic penguins" /> <meta name="twitter:description" content="In birds, possible explanations for a bias in brood sex ratio include differential cost of rearing nestlings of different sexes, and different parental fitness returns related to offspring sex. 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We studied brood sex ratio of Magellanic penguins," /> <title>(PDF) Sex-specific costs of rearing a nestling and its implications in the brood sex ratio of Magellanic penguins | Javier Ciancio - Academia.edu</title> <link rel="canonical" href="https://www.academia.edu/91287099/Sex_specific_costs_of_rearing_a_nestling_and_its_implications_in_the_brood_sex_ratio_of_Magellanic_penguins" /> <script async src="https://www.googletagmanager.com/gtag/js?id=G-5VKX33P2DS"></script> <script> window.dataLayer = window.dataLayer || []; function gtag(){dataLayer.push(arguments);} gtag('js', new Date()); gtag('config', 'G-5VKX33P2DS', { cookie_domain: 'academia.edu', send_page_view: false, }); gtag('event', 'page_view', { 'controller': "single_work", 'action': "show", 'controller_action': 'single_work#show', 'logged_in': 'false', 'edge': 'unknown', // Send nil if there is no A/B test bucket, in case some records get logged // with missing data - that way we can distinguish between the two cases. // ab_test_bucket should be of the form <ab_test_name>:<bucket> 'ab_test_bucket': null, }) </script> <script> var $controller_name = 'single_work'; var $action_name = "show"; var $rails_env = 'production'; var $app_rev = '93c3600233abd205de9146de3d5cceda5e30ac0b'; var $domain = 'academia.edu'; var $app_host = "academia.edu"; var $asset_host = "academia-assets.com"; var $start_time = new Date().getTime(); var $recaptcha_key = "6LdxlRMTAAAAADnu_zyLhLg0YF9uACwz78shpjJB"; var $recaptcha_invisible_key = "6Lf3KHUUAAAAACggoMpmGJdQDtiyrjVlvGJ6BbAj"; var $disableClientRecordHit = false; </script> <script> window.require = { config: function() { return function() {} } } </script> <script> window.Aedu = window.Aedu || {}; window.Aedu.hit_data = null; window.Aedu.serverRenderTime = new Date(1734132789000); window.Aedu.timeDifference = new Date().getTime() - 1734132789000; </script> <script type="application/ld+json">{"@context":"https://schema.org","@type":"ScholarlyArticle","abstract":"In birds, possible explanations for a bias in brood sex ratio include differential cost of rearing nestlings of different sexes, and different parental fitness returns related to offspring sex. We studied brood sex ratio of Magellanic penguins, Spheniscus magellanicus, in Puerto Deseado for 3 years. Our objectives were to compare the growth curves and energetic costs of rearing nestlings of different sexes, and to evaluate the possible implications of environmental and parental condition in the establishment of a bias in the brood sex ratio. We also investigated the relationship between hatching order and sex, and its impact on brood survival. Asymptotic mass was 11.41% higher for males than for females. The energetic cost of feeding male nestlings was slightly higher than for feeding females, but the difference in energy requirements was only 2.6% of the total energy budget. During the 3 years, brood sex ratio was 0.53, and almost constant within years over the raising period, showing no sex allocation during feeding. Sea surface temperature, which is linked to higher prey abundance when colder, explained brood sex ratio at fledging. The sex ratio was male-biased during the coldest year. Parental body condition was not an important variable explaining brood sex ratio. There was no bias in nestling sex with respect to hatching order and nestling survival was not related to nestling sex. We conclude that, even though the cost of feeding male offspring is higher, it only involves a small fraction of total cost of raising nestlings and might not be responsible for an adaptive bias in the sex ratio of nestlings for this species. However, during good oceanic conditions, females might bias their brood sex ratio towards males, thereby potentially gaining an advantage by raising good-quality males.","author":[{"@context":"https://schema.org","@type":"Person","name":"Javier Ciancio"}],"contributor":[],"dateCreated":"2022-11-21","headline":"Sex-specific costs of rearing a nestling and its implications in the brood sex ratio of Magellanic penguins","image":"https://attachments.academia-assets.com/94613398/thumbnails/1.jpg","inLanguage":"en","keywords":[],"publisher":{"@context":"https://schema.org","@type":"Organization","name":null},"sourceOrganization":[{"@context":"https://schema.org","@type":"EducationalOrganization","name":"conicet"}],"thumbnailUrl":"https://attachments.academia-assets.com/94613398/thumbnails/1.jpg","url":"https://www.academia.edu/91287099/Sex_specific_costs_of_rearing_a_nestling_and_its_implications_in_the_brood_sex_ratio_of_Magellanic_penguins"}</script><link rel="stylesheet" media="all" 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"https://www.academia.edu/login?post_login_redirect_url=https%3A%2F%2Fwww.academia.edu%2F91287099%2FSex_specific_costs_of_rearing_a_nestling_and_its_implications_in_the_brood_sex_ratio_of_Magellanic_penguins%3Fauto%3Ddownload"; window.loswp.translateUrl = "https://www.academia.edu/login?post_login_redirect_url=https%3A%2F%2Fwww.academia.edu%2F91287099%2FSex_specific_costs_of_rearing_a_nestling_and_its_implications_in_the_brood_sex_ratio_of_Magellanic_penguins%3Fshow_translation%3Dtrue"; window.loswp.previewableAttachments = [{"id":94613398,"identifier":"Attachment_94613398","shouldShowBulkDownload":false}]; window.loswp.shouldDetectTimezone = true; window.loswp.shouldShowBulkDownload = true; window.loswp.showSignupCaptcha = false window.loswp.willEdgeCache = false; window.loswp.work = {"work":{"id":91287099,"created_at":"2022-11-21T07:16:14.869-08:00","from_world_paper_id":null,"updated_at":"2022-11-21T07:39:39.779-08:00","_data":{"abstract":"In birds, possible explanations for a bias in brood sex ratio include differential cost of rearing nestlings of different sexes, and different parental fitness returns related to offspring sex. We studied brood sex ratio of Magellanic penguins, Spheniscus magellanicus, in Puerto Deseado for 3 years. Our objectives were to compare the growth curves and energetic costs of rearing nestlings of different sexes, and to evaluate the possible implications of environmental and parental condition in the establishment of a bias in the brood sex ratio. We also investigated the relationship between hatching order and sex, and its impact on brood survival. Asymptotic mass was 11.41% higher for males than for females. The energetic cost of feeding male nestlings was slightly higher than for feeding females, but the difference in energy requirements was only 2.6% of the total energy budget. During the 3 years, brood sex ratio was 0.53, and almost constant within years over the raising period, showing no sex allocation during feeding. Sea surface temperature, which is linked to higher prey abundance when colder, explained brood sex ratio at fledging. The sex ratio was male-biased during the coldest year. Parental body condition was not an important variable explaining brood sex ratio. There was no bias in nestling sex with respect to hatching order and nestling survival was not related to nestling sex. We conclude that, even though the cost of feeding male offspring is higher, it only involves a small fraction of total cost of raising nestlings and might not be responsible for an adaptive bias in the sex ratio of nestlings for this species. However, during good oceanic conditions, females might bias their brood sex ratio towards males, thereby potentially gaining an advantage by raising good-quality males."},"document_type":"paper","pre_hit_view_count_baseline":null,"quality":"high","language":"en","title":"Sex-specific costs of rearing a nestling and its implications in the brood sex ratio of Magellanic penguins","broadcastable":false,"draft":null,"has_indexable_attachment":true,"indexable":true}}["work"]; window.loswp.workCoauthors = [56809120]; window.loswp.locale = "en"; window.loswp.countryCode = "SG"; window.loswp.cwvAbTestBucket = ""; window.loswp.designVariant = "ds_vanilla"; window.loswp.fullPageMobileSutdModalVariant = "full_page_mobile_sutd_modal"; window.loswp.useOptimizedScribd4genScript = false; window.loginModal = {}; window.loginModal.appleClientId = 'edu.academia.applesignon';</script><script defer="" src="https://accounts.google.com/gsi/client"></script><div class="ds-loswp-container"><div class="ds-work-card--grid-container"><div class="ds-work-card--container js-loswp-work-card"><div class="ds-work-card--cover"><div class="ds-work-cover--wrapper"><div class="ds-work-cover--container"><button class="ds-work-cover--clickable js-swp-download-button" data-signup-modal="{"location":"swp-splash-paper-cover","attachmentId":94613398,"attachmentType":"pdf"}"><img alt="First page of “Sex-specific costs of rearing a nestling and its implications in the brood sex ratio of Magellanic penguins”" class="ds-work-cover--cover-thumbnail" src="https://0.academia-photos.com/attachment_thumbnails/94613398/mini_magick20221121-1-ap4dqv.png?1669040884" /><img alt="PDF Icon" class="ds-work-cover--file-icon" src="//a.academia-assets.com/images/single_work_splash/adobe_icon.svg" /><div class="ds-work-cover--hover-container"><span class="material-symbols-outlined" style="font-size: 20px" translate="no">download</span><p>Download Free PDF</p></div><div class="ds-work-cover--ribbon-container">Download Free PDF</div><div class="ds-work-cover--ribbon-triangle"></div></button></div></div></div><div class="ds-work-card--work-information"><h1 class="ds-work-card--work-title">Sex-specific costs of rearing a nestling and its implications in the brood sex ratio of Magellanic penguins</h1><div class="ds-work-card--work-authors ds-work-card--detail"><a class="ds-work-card--author js-wsj-grid-card-author ds2-5-body-md ds2-5-body-link" data-author-id="56809120" href="https://conicet.academia.edu/JavierCiancio"><img alt="Profile image of Javier Ciancio" class="ds-work-card--author-avatar" src="https://0.academia-photos.com/56809120/21304801/20727779/s65_javier.ciancio.jpg" />Javier Ciancio</a></div><div class="ds-work-card--detail"><div class="ds-work-card--work-metadata"><div class="ds-work-card--work-metadata__stat"><span class="material-symbols-outlined" style="font-size: 20px" translate="no">visibility</span><p class="ds2-5-body-sm" id="work-metadata-view-count">…</p></div><div class="ds-work-card--work-metadata__stat"><span class="material-symbols-outlined" style="font-size: 20px" translate="no">description</span><p class="ds2-5-body-sm">14 pages</p></div><div class="ds-work-card--work-metadata__stat"><span class="material-symbols-outlined" style="font-size: 20px" translate="no">link</span><p class="ds2-5-body-sm">1 file</p></div></div><script>(async () => { const workId = 91287099; 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if (!viewCountBody) { throw new Error('Failed to find work views element'); } viewCountBody.textContent = `${commaizedViewCount} views`; } catch (error) { // Remove the whole views element if there was some issue parsing. document.getElementById('work-metadata-view-count')?.parentNode?.remove(); throw new Error(`Failed to parse view count: ${viewCount}`, error); } }; // If the DOM is still loading, wait for it to be ready before updating the view count. if (document.readyState === "loading") { document.addEventListener('DOMContentLoaded', () => { updateViewCount(viewCount); }); // Otherwise, just update it immediately. } else { updateViewCount(viewCount); } })();</script></div><p class="ds-work-card--work-abstract ds-work-card--detail ds2-5-body-md">In birds, possible explanations for a bias in brood sex ratio include differential cost of rearing nestlings of different sexes, and different parental fitness returns related to offspring sex. We studied brood sex ratio of Magellanic penguins, Spheniscus magellanicus, in Puerto Deseado for 3 years. Our objectives were to compare the growth curves and energetic costs of rearing nestlings of different sexes, and to evaluate the possible implications of environmental and parental condition in the establishment of a bias in the brood sex ratio. We also investigated the relationship between hatching order and sex, and its impact on brood survival. Asymptotic mass was 11.41% higher for males than for females. The energetic cost of feeding male nestlings was slightly higher than for feeding females, but the difference in energy requirements was only 2.6% of the total energy budget. During the 3 years, brood sex ratio was 0.53, and almost constant within years over the raising period, showing no sex allocation during feeding. Sea surface temperature, which is linked to higher prey abundance when colder, explained brood sex ratio at fledging. The sex ratio was male-biased during the coldest year. Parental body condition was not an important variable explaining brood sex ratio. There was no bias in nestling sex with respect to hatching order and nestling survival was not related to nestling sex. We conclude that, even though the cost of feeding male offspring is higher, it only involves a small fraction of total cost of raising nestlings and might not be responsible for an adaptive bias in the sex ratio of nestlings for this species. However, during good oceanic conditions, females might bias their brood sex ratio towards males, thereby potentially gaining an advantage by raising good-quality males.</p><div class="ds-work-card--button-container"><button class="ds2-5-button js-swp-download-button" data-signup-modal="{"location":"continue-reading-button--work-card","attachmentId":94613398,"attachmentType":"pdf","workUrl":"https://www.academia.edu/91287099/Sex_specific_costs_of_rearing_a_nestling_and_its_implications_in_the_brood_sex_ratio_of_Magellanic_penguins"}">See full PDF</button><button class="ds2-5-button ds2-5-button--secondary js-swp-download-button" data-signup-modal="{"location":"download-pdf-button--work-card","attachmentId":94613398,"attachmentType":"pdf","workUrl":"https://www.academia.edu/91287099/Sex_specific_costs_of_rearing_a_nestling_and_its_implications_in_the_brood_sex_ratio_of_Magellanic_penguins"}"><span class="material-symbols-outlined" style="font-size: 20px" translate="no">download</span>Download PDF</button></div></div></div></div><div data-auto_select="false" data-client_id="331998490334-rsn3chp12mbkiqhl6e7lu2q0mlbu0f1b" data-doc_id="94613398" data-landing_url="https://www.academia.edu/91287099/Sex_specific_costs_of_rearing_a_nestling_and_its_implications_in_the_brood_sex_ratio_of_Magellanic_penguins" data-login_uri="https://www.academia.edu/registrations/google_one_tap" data-moment_callback="onGoogleOneTapEvent" id="g_id_onload"></div><div class="ds-top-related-works--grid-container"><div class="ds-related-content--container ds-top-related-works--container"><h2 class="ds-related-content--heading">Related papers</h2><div class="ds-related-work--container js-wsj-grid-card" data-collection-position="0" data-entity-id="14180791" data-sort-order="default"><a class="ds-related-work--title js-wsj-grid-card-title ds2-5-body-md ds2-5-body-link" href="https://www.academia.edu/14180791/Variably_male_biased_sex_ratio_in_a_marine_bird_with_females_larger_than_males">Variably male-biased sex ratio in a marine bird with females larger than males</a><div class="ds-related-work--metadata"><a class="js-wsj-grid-card-author ds2-5-body-sm ds2-5-body-link" data-author-id="33163692" href="https://unam.academia.edu/HughDrummond">Hugh Drummond</a></div><p class="ds-related-work--metadata ds2-5-body-xs">Oecologia, 1999</p><p class="ds-related-work--abstract ds2-5-body-sm">When the costs of rearing males and females dier progeny sex ratios are expected to be biased toward the less expensive sex. Blue-footed booby (Sula nebouxii) females are larger and roughly 32% heavier than males, thus presumably more costly to rear. We recorded hatching and¯edging sex ratios in 1989, and edging sex ratios during the next 5 years. In 1989, the sample of 751 chicks showed male bias at hatching (56%) and at¯edging (57% at~90 days). Fledging sex ratios during the ®ve subsequent reproductive seasons were at unity (1 year) or male-biased, varying from 56% to 70%. Male bias was greater during years when mean sea surface temperature was warmer and food was presumably in short supply. During two warm-water years (only)¯edging sex ratio varied with hatching date. Proportions of male¯edglings increased with date from 0.48 to 0.73 in 1994, and from 0.33 to 0.79 in 1995. Similar results were obtained when the analysis was repeated using only broods with no nestling mortality, suggesting that the overall increase in the proportion of males over the season was the result of sex ratio adjustments at hatching. The male-biased sex ratio, and the increased male bias during poor breeding conditions supports the idea that daughters may be more costly than sons, and that their relative cost increases in poor conditions.</p><div class="ds-related-work--ctas"><button class="ds2-5-text-link ds2-5-text-link--inline js-swp-download-button" data-signup-modal="{"location":"wsj-grid-card-download-pdf-modal","work_title":"Variably male-biased sex ratio in a marine bird with females larger than males","attachmentId":44529454,"attachmentType":"pdf","work_url":"https://www.academia.edu/14180791/Variably_male_biased_sex_ratio_in_a_marine_bird_with_females_larger_than_males","alternativeTracking":true}"><span class="material-symbols-outlined" style="font-size: 18px" translate="no">download</span><span class="ds2-5-text-link__content">Download free PDF</span></button><a class="ds2-5-text-link ds2-5-text-link--inline js-wsj-grid-card-view-pdf" href="https://www.academia.edu/14180791/Variably_male_biased_sex_ratio_in_a_marine_bird_with_females_larger_than_males"><span class="ds2-5-text-link__content">View PDF</span><span class="material-symbols-outlined" style="font-size: 18px" translate="no">chevron_right</span></a></div></div><div class="ds-related-work--container js-wsj-grid-card" data-collection-position="1" data-entity-id="452663" data-sort-order="default"><a class="ds-related-work--title js-wsj-grid-card-title ds2-5-body-md ds2-5-body-link" href="https://www.academia.edu/452663/Sex_Allocation_In_a_Monomorphic_Seabird_With_a_Single_Egg_Clutch_Test_of_the_Environment_Mate_Quality_and_Female_Condition_Hypotheses">Sex Allocation In a Monomorphic Seabird With a Single-Egg Clutch: Test of the Environment, Mate Quality, and Female Condition Hypotheses</a><div class="ds-related-work--metadata"><a class="js-wsj-grid-card-author ds2-5-body-sm ds2-5-body-link" data-author-id="207484" href="https://westernsydney.academia.edu/BriAnneAddison">BriAnne Addison</a></div><p class="ds-related-work--metadata ds2-5-body-xs">Behavioral Ecology and …, 2008</p><div class="ds-related-work--ctas"><button class="ds2-5-text-link ds2-5-text-link--inline js-swp-download-button" data-signup-modal="{"location":"wsj-grid-card-download-pdf-modal","work_title":"Sex Allocation In a Monomorphic Seabird With a Single-Egg Clutch: Test of the Environment, Mate Quality, and Female Condition Hypotheses","attachmentId":3443110,"attachmentType":"pdf","work_url":"https://www.academia.edu/452663/Sex_Allocation_In_a_Monomorphic_Seabird_With_a_Single_Egg_Clutch_Test_of_the_Environment_Mate_Quality_and_Female_Condition_Hypotheses","alternativeTracking":true}"><span class="material-symbols-outlined" style="font-size: 18px" translate="no">download</span><span class="ds2-5-text-link__content">Download free PDF</span></button><a class="ds2-5-text-link ds2-5-text-link--inline js-wsj-grid-card-view-pdf" href="https://www.academia.edu/452663/Sex_Allocation_In_a_Monomorphic_Seabird_With_a_Single_Egg_Clutch_Test_of_the_Environment_Mate_Quality_and_Female_Condition_Hypotheses"><span class="ds2-5-text-link__content">View PDF</span><span class="material-symbols-outlined" style="font-size: 18px" translate="no">chevron_right</span></a></div></div><div class="ds-related-work--container js-wsj-grid-card" data-collection-position="2" data-entity-id="27152841" data-sort-order="default"><a class="ds-related-work--title js-wsj-grid-card-title ds2-5-body-md ds2-5-body-link" href="https://www.academia.edu/27152841/Identifying_the_selective_pressures_underlying_offspring_sex_ratio_adjustments_a_case_study_in_a_wild_seabird">Identifying the selective pressures underlying offspring sex-ratio adjustments: a case study in a wild seabird</a><div class="ds-related-work--metadata"><a class="js-wsj-grid-card-author ds2-5-body-sm ds2-5-body-link" data-author-id="5928060" href="https://aberdeen.academia.edu/JohnSpeakman">John Speakman</a></div><p class="ds-related-work--metadata ds2-5-body-xs">Behavioral Ecology, 2015</p><p class="ds-related-work--abstract ds2-5-body-sm">Sex allocation theory predicts that parents should bias offspring sex according to the costs and benefits associated with producing either sex in a given context. Accurately interpreting sex-ratio biases, therefore, requires a precise identification of these selective pressures. However, such information is generally lacking. This may partly explain the inconsistency in reported sex allocation patterns, especially in vertebrates. We present data from a long-term feeding experiment in black-legged kittiwakes (Rissa tridactyla) that allowed us to increase investment capacity for some breeding pairs. Previous findings showed that these pairs then overproduced sons compared with control parents. Here, our aim was to test the underlying assumptions of the 2 appropriate sex allocation models for our context: the "cost of reproduction hypothesis" and the "Trivers-Willard hypothesis." The former assumes a sex difference in rearing costs, whereas the latter assumes a difference in fitness returns. 1) Independent of feeding treatment, rearing sons was energetically more demanding for parents (as revealed by higher energy expenditure and higher baseline corticosterone levels) than rearing daughters, thereby corroborating the underlying assumption of the "cost of reproduction hypothesis." 2) Evidence supporting the assumptions of the "Trivers-Willard hypothesis" was less convincing. Overall, our results suggest that drivers of parental sex allocation decisions are probably more related to offspring sex-specific energetic costs than to their future reproductive success in our study species. Assessing the adaptive value of sex-ratio biases requires precise investigation of the assumptions underlying theoretical models, particularly as long as the mechanisms involved in sex-ratio manipulation remain largely unknown.</p><div class="ds-related-work--ctas"><button class="ds2-5-text-link ds2-5-text-link--inline js-swp-download-button" data-signup-modal="{"location":"wsj-grid-card-download-pdf-modal","work_title":"Identifying the selective pressures underlying offspring sex-ratio adjustments: a case study in a wild seabird","attachmentId":47402953,"attachmentType":"pdf","work_url":"https://www.academia.edu/27152841/Identifying_the_selective_pressures_underlying_offspring_sex_ratio_adjustments_a_case_study_in_a_wild_seabird","alternativeTracking":true}"><span class="material-symbols-outlined" style="font-size: 18px" translate="no">download</span><span class="ds2-5-text-link__content">Download free PDF</span></button><a class="ds2-5-text-link ds2-5-text-link--inline js-wsj-grid-card-view-pdf" href="https://www.academia.edu/27152841/Identifying_the_selective_pressures_underlying_offspring_sex_ratio_adjustments_a_case_study_in_a_wild_seabird"><span class="ds2-5-text-link__content">View PDF</span><span class="material-symbols-outlined" style="font-size: 18px" translate="no">chevron_right</span></a></div></div><div class="ds-related-work--container js-wsj-grid-card" data-collection-position="3" data-entity-id="114722733" data-sort-order="default"><a class="ds-related-work--title js-wsj-grid-card-title ds2-5-body-md ds2-5-body-link" href="https://www.academia.edu/114722733/Sex_ratio_is_variable_and_increasingly_male_biased_at_two_colonies_of_Magellanic_Penguins">Sex ratio is variable and increasingly male biased at two colonies of Magellanic Penguins</a><div class="ds-related-work--metadata"><a class="js-wsj-grid-card-author ds2-5-body-sm ds2-5-body-link" data-author-id="7754597" href="https://cenpat.academia.edu/PabloGarciaBorboroglu">Pablo Garcia Borboroglu</a></div><p class="ds-related-work--metadata ds2-5-body-xs">Ecology, 2020</p><p class="ds-related-work--abstract ds2-5-body-sm">Sex ratios are commonly skewed and variable in wild populations, but few studies track temporal trends in this demographic parameter. We examined variation in the operational sex ratio at two protected and declining breeding colonies of Magellanic Penguins (Spheniscus magellanicus) in Chubut, Argentina. Penguins from the two colonies, separated by 105 km, migrate north in the non-breeding season and have overlapping distributions at sea. Conditions during the non-breeding season can impact long-term trends in operational sex ratio (i.e., through sex-specific survival) and interannual variation in operational sex ratio (i.e., through sex-specific breeding decisions). We found an increasingly male-biased operational sex ratio at the two disparate colonies of Magellanic Penguins, which may contribute to continued population decline. We also found that the two colonies showed synchronous interannual variation in operational sex ratio, driven by variation in the number of females present each year. This pattern may be linked to sex-specific overwintering effects that cause females to skip breeding, i.e., to remain at sea rather than returning to the colony to breed, more often than males. Contrary to our predictions, colony-wide reproductive success was not lower in years with a more male-biased operational sex ratio. We did find that males showed more evidence of fighting and were less likely to pair when the operational sex ratio was more male biased. Our results highlight an indirect mechanism through which variation in the operational sex ratio can influence populations, through a higher incidence of fighting among the less abundant sex. Because biased sex ratios can reduce the size of the breeding population and influence rates of conflict, tracking operational sex ratio is critical for conservation.</p><div class="ds-related-work--ctas"><button class="ds2-5-text-link ds2-5-text-link--inline js-swp-download-button" data-signup-modal="{"location":"wsj-grid-card-download-pdf-modal","work_title":"Sex ratio is variable and increasingly male biased at two colonies of Magellanic Penguins","attachmentId":111342311,"attachmentType":"pdf","work_url":"https://www.academia.edu/114722733/Sex_ratio_is_variable_and_increasingly_male_biased_at_two_colonies_of_Magellanic_Penguins","alternativeTracking":true}"><span class="material-symbols-outlined" style="font-size: 18px" translate="no">download</span><span class="ds2-5-text-link__content">Download free PDF</span></button><a class="ds2-5-text-link ds2-5-text-link--inline js-wsj-grid-card-view-pdf" href="https://www.academia.edu/114722733/Sex_ratio_is_variable_and_increasingly_male_biased_at_two_colonies_of_Magellanic_Penguins"><span class="ds2-5-text-link__content">View PDF</span><span class="material-symbols-outlined" style="font-size: 18px" translate="no">chevron_right</span></a></div></div><div class="ds-related-work--container js-wsj-grid-card" data-collection-position="4" data-entity-id="8035922" data-sort-order="default"><a class="ds-related-work--title js-wsj-grid-card-title ds2-5-body-md ds2-5-body-link" href="https://www.academia.edu/8035922/Male_biased_reproductive_effort_in_a_long_lived_seabird">Male-biased reproductive effort in a long-lived seabird</a><div class="ds-related-work--metadata"><a class="js-wsj-grid-card-author ds2-5-body-sm ds2-5-body-link" data-author-id="15451418" href="https://bucknell.academia.edu/MarkHaussmann">Mark Haussmann</a></div><p class="ds-related-work--abstract ds2-5-body-sm">In dimorphic seabirds, the larger sex tends to provision more than the smaller sex. In contrast, monogamy and biparental care are often associated with equal effort between the sexes. However, the few studies that have tested sex-specific effort in monomorphic seabirds have primarily examined the details of foraging at sea.</p><div class="ds-related-work--ctas"><button class="ds2-5-text-link ds2-5-text-link--inline js-swp-download-button" data-signup-modal="{"location":"wsj-grid-card-download-pdf-modal","work_title":"Male-biased reproductive effort in a long-lived seabird","attachmentId":34497042,"attachmentType":"pdf","work_url":"https://www.academia.edu/8035922/Male_biased_reproductive_effort_in_a_long_lived_seabird","alternativeTracking":true}"><span class="material-symbols-outlined" style="font-size: 18px" translate="no">download</span><span class="ds2-5-text-link__content">Download free PDF</span></button><a class="ds2-5-text-link ds2-5-text-link--inline js-wsj-grid-card-view-pdf" href="https://www.academia.edu/8035922/Male_biased_reproductive_effort_in_a_long_lived_seabird"><span class="ds2-5-text-link__content">View PDF</span><span class="material-symbols-outlined" style="font-size: 18px" translate="no">chevron_right</span></a></div></div><div class="ds-related-work--container js-wsj-grid-card" data-collection-position="5" data-entity-id="21859383" data-sort-order="default"><a class="ds-related-work--title js-wsj-grid-card-title ds2-5-body-md ds2-5-body-link" href="https://www.academia.edu/21859383/Food_availability_and_offspring_sex_in_a_monogamous_seabird_insights_from_an_experimental_approach">Food availability and offspring sex in a monogamous seabird: insights from an experimental approach</a><div class="ds-related-work--metadata"><a class="js-wsj-grid-card-author ds2-5-body-sm ds2-5-body-link" data-author-id="43094655" href="https://cnrs.academia.edu/EtienneDanchin">Etienne Danchin</a></div><p class="ds-related-work--metadata ds2-5-body-xs">Behavioral Ecology, 2012</p><p class="ds-related-work--abstract ds2-5-body-sm">Sex allocation theory predicts that parents should favor offspring of the sex that provides the greatest fitness return. Despite growing evidence suggesting that vertebrates are able to overcome the constraint of chromosomal sex determination, the general pattern remains equivocal, indicating a need for experimental investigations. We used an experimental feeding design to study sex allocation during 3 years in black-legged kittiwakes (Rissa tridactyla). Intense male-male competition for securing a breeding site is common in this species in which males are heavier and larger than females. Hence, we hypothesized that parents producing fledglings in better than average condition, as supplementarily fed pairs do, would increase their fitness return by producing sons. Conversely, producing daughters would be a better tactic for Unfed parents. Hence, we predicted that Fed parents produce more sons than Unfed parents. This prediction is particularly expected if sexual dimorphism arises as early as during chick rearing, suggesting strong selective pressures for optimal male development. Our results showed that 1) males were heavier and larger than females prior to fledging and that 2) Fed parents produced relatively more male hatchlings than Unfed parents. We interpret this result in terms of a Trivers-Willard-type process. Furthermore, our data revealed that Unfed parents significantly overproduced female hatchlings, whereas offspring sex ratio was balanced among Fed parents. Because the 3 reproductive seasons we considered were particularly poor food years, Unfed parents may have overproduced daughters to avoid the apparent higher reproductive costs of raising sons.</p><div class="ds-related-work--ctas"><button class="ds2-5-text-link ds2-5-text-link--inline js-swp-download-button" data-signup-modal="{"location":"wsj-grid-card-download-pdf-modal","work_title":"Food availability and offspring sex in a monogamous seabird: insights from an experimental approach","attachmentId":42602841,"attachmentType":"pdf","work_url":"https://www.academia.edu/21859383/Food_availability_and_offspring_sex_in_a_monogamous_seabird_insights_from_an_experimental_approach","alternativeTracking":true}"><span class="material-symbols-outlined" style="font-size: 18px" translate="no">download</span><span class="ds2-5-text-link__content">Download free PDF</span></button><a class="ds2-5-text-link ds2-5-text-link--inline js-wsj-grid-card-view-pdf" href="https://www.academia.edu/21859383/Food_availability_and_offspring_sex_in_a_monogamous_seabird_insights_from_an_experimental_approach"><span class="ds2-5-text-link__content">View PDF</span><span class="material-symbols-outlined" style="font-size: 18px" translate="no">chevron_right</span></a></div></div><div class="ds-related-work--container js-wsj-grid-card" data-collection-position="6" data-entity-id="121063284" data-sort-order="default"><a class="ds-related-work--title js-wsj-grid-card-title ds2-5-body-md ds2-5-body-link" href="https://www.academia.edu/121063284/Inter_Annual_Variability_of_Fledgling_Sex_Ratio_in_King_Penguins">Inter-Annual Variability of Fledgling Sex Ratio in King Penguins</a><div class="ds-related-work--metadata"><a class="js-wsj-grid-card-author ds2-5-body-sm ds2-5-body-link" data-author-id="309346838" href="https://independent.academia.edu/C%C3%A9liaBordier">Célia Bordier</a></div><p class="ds-related-work--metadata ds2-5-body-xs">PLoS ONE, 2014</p><p class="ds-related-work--abstract ds2-5-body-sm">As the number of breeding pairs depends on the adult sex ratio in a monogamous species with biparental care, investigating sex-ratio variability in natural populations is essential to understand population dynamics. Using 10 years of data (2000-2009) in a seasonally monogamous seabird, the king penguin (Aptenodytes patagonicus), we investigated the annual sex ratio at fledging, and the potential environmental causes for its variation. Over more than 4000 birds, the annual sex ratio at fledging was highly variable (ranging from 44.4% to 58.3% of males), and on average slightly biased towards males (51.6%). Yearly variation in sex-ratio bias was neither related to density within the colony, nor to global or local oceanographic conditions known to affect both the productivity and accessibility of penguin foraging areas. However, rising sea surface temperature coincided with an increase in fledging sex-ratio variability. Fledging sex ratio was also correlated with difference in body condition between male and female fledglings. When more males were produced in a given year, their body condition was higher (and reciprocally), suggesting that parents might adopt a sex-biased allocation strategy depending on yearly environmental conditions and/or that the effect of environmental parameters on chick condition and survival may be sex-dependent. The initial bias in sex ratio observed at the juvenile stage tended to return to 1:1 equilibrium upon first breeding attempts, as would be expected from Fisher's classic theory of offspring sex-ratio variation.</p><div class="ds-related-work--ctas"><button class="ds2-5-text-link ds2-5-text-link--inline js-swp-download-button" data-signup-modal="{"location":"wsj-grid-card-download-pdf-modal","work_title":"Inter-Annual Variability of Fledgling Sex Ratio in King Penguins","attachmentId":116040307,"attachmentType":"pdf","work_url":"https://www.academia.edu/121063284/Inter_Annual_Variability_of_Fledgling_Sex_Ratio_in_King_Penguins","alternativeTracking":true}"><span class="material-symbols-outlined" style="font-size: 18px" translate="no">download</span><span class="ds2-5-text-link__content">Download free PDF</span></button><a class="ds2-5-text-link ds2-5-text-link--inline js-wsj-grid-card-view-pdf" href="https://www.academia.edu/121063284/Inter_Annual_Variability_of_Fledgling_Sex_Ratio_in_King_Penguins"><span class="ds2-5-text-link__content">View PDF</span><span class="material-symbols-outlined" style="font-size: 18px" translate="no">chevron_right</span></a></div></div><div class="ds-related-work--container js-wsj-grid-card" data-collection-position="7" data-entity-id="83702928" data-sort-order="default"><a class="ds-related-work--title js-wsj-grid-card-title ds2-5-body-md ds2-5-body-link" href="https://www.academia.edu/83702928/Are_female_offspring_from_a_single_egg_seabird_more_costly_to_raise">Are female offspring from a single-egg seabird more costly to raise?</a><div class="ds-related-work--metadata"><a class="js-wsj-grid-card-author ds2-5-body-sm ds2-5-body-link" data-author-id="37142589" href="https://independent.academia.edu/KjellErikstad">Kjell E Erikstad</a></div><p class="ds-related-work--metadata ds2-5-body-xs">Behavioral Ecology, 2012</p><p class="ds-related-work--abstract ds2-5-body-sm">If the fitness benefits gained from producing male and female offspring differ due to parental or environmental conditions, parents should adjust their level of investment accordingly. We studied sex allocation and reproductive investment in a population of common guillemots (Uria aalge) in 2 breeding seasons. The common guillemot is a single-egg species and the male is only slightly larger than the female implying small, if any differential costs of raising male and female offspring. We use 4 variables to characterize reproductive allocation: 1) sex of the chick at hatching, 2) adult male and female body condition, 3) baseline corticosterone (CORT) level of adults early and late in the chick-rearing period, and 4) body mass of the chicks just prior to fledging. Females that produced female offspring were in better body condition during early chick-rearing than those producing males and both parents raising a female offspring lost more body mass during the chick-rearing period. Female offspring were heavier than male offspring at the end of the chick-rearing period. Whereas hatching sex ratio was at unity in one of the years, it was strongly skewed toward females (72.5%) in the other year, and this pattern was consistent for a subset of pairs studied in both years. Early baseline CORT levels of adults were lower in the year when the sex ratio was skewed toward female offspring. We discuss this unexpected pattern of sex allocation in relation to variation in feeding conditions and the role of females in competing for good nesting sites.</p><div class="ds-related-work--ctas"><button class="ds2-5-text-link ds2-5-text-link--inline js-swp-download-button" data-signup-modal="{"location":"wsj-grid-card-download-pdf-modal","work_title":"Are female offspring from a single-egg seabird more costly to raise?","attachmentId":88960866,"attachmentType":"pdf","work_url":"https://www.academia.edu/83702928/Are_female_offspring_from_a_single_egg_seabird_more_costly_to_raise","alternativeTracking":true}"><span class="material-symbols-outlined" style="font-size: 18px" translate="no">download</span><span class="ds2-5-text-link__content">Download free PDF</span></button><a class="ds2-5-text-link ds2-5-text-link--inline js-wsj-grid-card-view-pdf" href="https://www.academia.edu/83702928/Are_female_offspring_from_a_single_egg_seabird_more_costly_to_raise"><span class="ds2-5-text-link__content">View PDF</span><span class="material-symbols-outlined" style="font-size: 18px" translate="no">chevron_right</span></a></div></div><div class="ds-related-work--container js-wsj-grid-card" data-collection-position="8" data-entity-id="93377454" data-sort-order="default"><a class="ds-related-work--title js-wsj-grid-card-title ds2-5-body-md ds2-5-body-link" href="https://www.academia.edu/93377454/Nest_size_and_hatchling_sex_ratio_in_chinstrap_penguins">Nest size and hatchling sex ratio in chinstrap penguins</a><div class="ds-related-work--metadata"><a class="js-wsj-grid-card-author ds2-5-body-sm ds2-5-body-link" data-author-id="116210016" href="https://independent.academia.edu/AnaLe%C3%B3n42">Ana León</a></div><p class="ds-related-work--metadata ds2-5-body-xs">Polar Biology, 2004</p><p class="ds-related-work--abstract ds2-5-body-sm">Variation in the sex ratio at hatching in the chinstrap penguin Pygoscelis antarctica was investigated, using molecular sexing to test predictions of sex allocation theory. The sex ratio was slightly male-biased (0.54) but did not differ significantly from parity. The proportion of males increased with nest size, an estimator of parental quality in chinstrap penguins. Highquality parents were able to produce and rear a higher proportion of male offspring, the more costly sex in this slightly sexually dimorphic species. Our results may be in agreement with Trivers and Willard's (1973) argument on biases in the offspring sex ratio being contingent on parental condition or quality.</p><div class="ds-related-work--ctas"><button class="ds2-5-text-link ds2-5-text-link--inline js-swp-download-button" data-signup-modal="{"location":"wsj-grid-card-download-pdf-modal","work_title":"Nest size and hatchling sex ratio in chinstrap penguins","attachmentId":96131714,"attachmentType":"pdf","work_url":"https://www.academia.edu/93377454/Nest_size_and_hatchling_sex_ratio_in_chinstrap_penguins","alternativeTracking":true}"><span class="material-symbols-outlined" style="font-size: 18px" translate="no">download</span><span class="ds2-5-text-link__content">Download free PDF</span></button><a class="ds2-5-text-link ds2-5-text-link--inline js-wsj-grid-card-view-pdf" href="https://www.academia.edu/93377454/Nest_size_and_hatchling_sex_ratio_in_chinstrap_penguins"><span class="ds2-5-text-link__content">View PDF</span><span class="material-symbols-outlined" style="font-size: 18px" translate="no">chevron_right</span></a></div></div><div class="ds-related-work--container js-wsj-grid-card" data-collection-position="9" data-entity-id="2401833" data-sort-order="default"><a class="ds-related-work--title js-wsj-grid-card-title ds2-5-body-md ds2-5-body-link" href="https://www.academia.edu/2401833/Male_chicks_are_more_costly_to_rear_than_females_in_a_monogamous_seabird_the_Common_Murre">Male chicks are more costly to rear than females in a monogamous seabird, the Common Murre</a><div class="ds-related-work--metadata"><a class="js-wsj-grid-card-author ds2-5-body-sm ds2-5-body-link" data-author-id="3119651" href="https://independent.academia.edu/CameronMaureen">Maureen Cameron</a></div><p class="ds-related-work--metadata ds2-5-body-xs">Behavioral Ecology, 2007</p><p class="ds-related-work--abstract ds2-5-body-sm">Feeding rates and mass loss during chick rearing were compared for individually marked parents of male and female Common Murre (Uria aalge) chicks at Great Island, Newfoundland, Canada, from 1997-2001. Both parents in this socially monogamous seabird species share parental care duties until colony departure, after which the single chick is fed only by its father. Because murres provision their single chicks with one clearly visible fish per trip, it is possible to accurately determine whether parents differentially feed male and female chicks. Based on slightly greater mass of males in adulthood, possibly favored by sex differences in breeding roles, we predicted that male nestlings would be fed more than females. Fathers' feeding rate to sons, but not daughters, increased with chick age, whereas maternal feeding rate increased with chick age for both sexes. When year-corrected feeding rates of pairs rearing both sexes were compared, both mothers and fathers fed their sons significantly more than their daughters in the later part of the chick-rearing period. Moreover, parents rearing male chicks lost mass at a significantly higher rate than those rearing females. There was no difference in fledging age for sons and daughters. These results indicate that differential parental allocation occurs and has measurable costs even in a species with only slight adult sexual dimorphism.</p><div class="ds-related-work--ctas"><button class="ds2-5-text-link ds2-5-text-link--inline js-swp-download-button" data-signup-modal="{"location":"wsj-grid-card-download-pdf-modal","work_title":"Male chicks are more costly to rear than females in a monogamous seabird, the Common Murre","attachmentId":50645101,"attachmentType":"pdf","work_url":"https://www.academia.edu/2401833/Male_chicks_are_more_costly_to_rear_than_females_in_a_monogamous_seabird_the_Common_Murre","alternativeTracking":true}"><span class="material-symbols-outlined" style="font-size: 18px" translate="no">download</span><span class="ds2-5-text-link__content">Download free PDF</span></button><a class="ds2-5-text-link ds2-5-text-link--inline js-wsj-grid-card-view-pdf" href="https://www.academia.edu/2401833/Male_chicks_are_more_costly_to_rear_than_females_in_a_monogamous_seabird_the_Common_Murre"><span class="ds2-5-text-link__content">View PDF</span><span class="material-symbols-outlined" style="font-size: 18px" translate="no">chevron_right</span></a></div></div></div></div><div class="ds-sticky-ctas--wrapper js-loswp-sticky-ctas hidden"><div class="ds-sticky-ctas--grid-container"><div class="ds-sticky-ctas--container"><button class="ds2-5-button js-swp-download-button" data-signup-modal="{"location":"continue-reading-button--sticky-ctas","attachmentId":94613398,"attachmentType":"pdf","workUrl":null}">See full PDF</button><button class="ds2-5-button ds2-5-button--secondary js-swp-download-button" data-signup-modal="{"location":"download-pdf-button--sticky-ctas","attachmentId":94613398,"attachmentType":"pdf","workUrl":null}"><span class="material-symbols-outlined" style="font-size: 20px" translate="no">download</span>Download PDF</button></div></div></div><div class="ds-below-fold--grid-container"><div class="ds-work--container js-loswp-embedded-document"><div class="attachment_preview" data-attachment="Attachment_94613398" style="display: none"><div class="js-scribd-document-container"><div class="scribd--document-loading js-scribd-document-loader" style="display: block;"><img alt="Loading..." src="//a.academia-assets.com/images/loaders/paper-load.gif" /><p>Loading Preview</p></div></div><div style="text-align: center;"><div class="scribd--no-preview-alert js-preview-unavailable"><p>Sorry, preview is currently unavailable. You can download the paper by clicking the button above.</p></div></div></div></div><div class="ds-sidebar--container js-work-sidebar"><div class="ds-related-content--container"><h2 class="ds-related-content--heading">Related papers</h2><div class="ds-related-work--container js-related-work-sidebar-card" data-collection-position="0" data-entity-id="88803711" data-sort-order="default"><a class="ds-related-work--title js-related-work-grid-card-title ds2-5-body-md ds2-5-body-link" href="https://www.academia.edu/88803711/Phenotypic_assortative_mating_and_within_pair_sexual_dimorphism_and_its_influence_on_breeding_success_and_offspring_quality_in_Magellanic_penguins">Phenotypic assortative mating and within-pair sexual dimorphism and its influence on breeding success and offspring quality in Magellanic penguins</a><div class="ds-related-work--metadata"><a class="js-related-work-grid-card-author ds2-5-body-sm ds2-5-body-link" data-author-id="241160278" href="https://independent.academia.edu/olgalorenacortesceballos">olga lorena cortes ceballos</a></div><p class="ds-related-work--metadata ds2-5-body-xs">Canadian Journal of Zoology, 2001</p><div class="ds-related-work--ctas"><button class="ds2-5-text-link ds2-5-text-link--inline js-swp-download-button" data-signup-modal="{"location":"wsj-grid-card-download-pdf-modal","work_title":"Phenotypic assortative mating and within-pair sexual dimorphism and its influence on breeding success and offspring quality in Magellanic penguins","attachmentId":92709802,"attachmentType":"pdf","work_url":"https://www.academia.edu/88803711/Phenotypic_assortative_mating_and_within_pair_sexual_dimorphism_and_its_influence_on_breeding_success_and_offspring_quality_in_Magellanic_penguins","alternativeTracking":true}"><span class="material-symbols-outlined" style="font-size: 18px" translate="no">download</span><span class="ds2-5-text-link__content">Download free PDF</span></button><a class="ds2-5-text-link ds2-5-text-link--inline js-related-work-grid-card-view-pdf" href="https://www.academia.edu/88803711/Phenotypic_assortative_mating_and_within_pair_sexual_dimorphism_and_its_influence_on_breeding_success_and_offspring_quality_in_Magellanic_penguins"><span class="ds2-5-text-link__content">View PDF</span><span class="material-symbols-outlined" style="font-size: 18px" translate="no">chevron_right</span></a></div></div><div class="ds-related-work--container js-related-work-sidebar-card" data-collection-position="1" data-entity-id="13595784" data-sort-order="default"><a class="ds-related-work--title js-related-work-grid-card-title ds2-5-body-md ds2-5-body-link" href="https://www.academia.edu/13595784/Parental_care_and_adaptive_brood_sex_ratio_manipulation_in_birds">Parental care and adaptive brood sex ratio manipulation in birds</a><div class="ds-related-work--metadata"><a class="js-related-work-grid-card-author ds2-5-body-sm ds2-5-body-link" data-author-id="32955626" href="https://lu.academia.edu/DHasselquist">D. Hasselquist</a><span>, </span><a class="js-related-work-grid-card-author ds2-5-body-sm ds2-5-body-link" data-author-id="32772040" href="https://iwww-mpg.academia.edu/BartKempenaers">Bart Kempenaers</a></div><p class="ds-related-work--metadata ds2-5-body-xs">Philosophical Transactions of the Royal Society B: Biological Sciences, 2002</p><div class="ds-related-work--ctas"><button class="ds2-5-text-link ds2-5-text-link--inline js-swp-download-button" data-signup-modal="{"location":"wsj-grid-card-download-pdf-modal","work_title":"Parental care and adaptive brood sex ratio manipulation in birds","attachmentId":45174916,"attachmentType":"pdf","work_url":"https://www.academia.edu/13595784/Parental_care_and_adaptive_brood_sex_ratio_manipulation_in_birds","alternativeTracking":true}"><span class="material-symbols-outlined" style="font-size: 18px" translate="no">download</span><span class="ds2-5-text-link__content">Download free PDF</span></button><a class="ds2-5-text-link 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