Smaller Clutches Research Articles

Evolutionary timelines help explain the evolution of parental care strategies.

Comparative research on the evolution of parental care has followed a general trend in recent years, with researchers gathering data on clutch size or egg size and correlating these traits with ecological variables across a phylogeny. The goal of these studies is to shed light on how and why certain strategies evolve. However, results vary across studies, and we rarely have results explaining why the observed pattern occurred, leaving us with further hypotheses to test. By using a combination of comparative methods, we provide an explanation of how such patterns emerge based on the evolutionary timeline of constructing burrows and the energy invested into egg size and egg number; this combination also allowed us to pinpoint why the pattern occurred. We do so with data on freshwater crayfish, which are ideal for such investigations because they vary in their reliance on burrows, their body size, and their investment into their offspring. Specifically, we tested whether a strong dependence on burrows is related to investment in eggs (i.e., larger eggs or more eggs) given the body size of the species. Surprisingly, we found no correlation between burrowing and the size or number of eggs crayfish lay; instead, body size was the best predictor of the number of eggs (but not the size of eggs) that each species lays. Interestingly, our analysis suggests that crayfish ancestors had a small clutch size, relatively large eggs, and a weak connection to burrows. Thus, the shift to heavily relying on burrows appeared after this lineage was already investing in large eggs, which gives insights into the colonization of freshwater by an ancestral astacidean ancestor. While other studies show that the evolution of parental care strategies is not straightforward, our study provides a clear evolutionary timeline of the interplay between the evolution of burrowing behavior and shifts in the evolution of egg investment. Furthermore, our work showcases how merging multiple phylogenetically informed approaches can disentangle the origin and evolution of life history traits.

Biological traits and biome features mediate responses of terrestrial bird demography to droughts.

Changing drought regimes are a rising threat to biodiversity, yet their impacts on wildlife vary greatly. Acknowledging the factors associated with these consequences brings novel insights into species vulnerability resulting from extreme climatic events and facilitates effective mitigation of climate change risks. Based on 319 observations from 29 peer-reviewed studies on birds-a well-monitored taxonomic group-we extract the responses of demographic metrics to droughts for 204 species across eight terrestrial biomes to examine the consequences of droughts. According to relevant studies, we chose the factors potentially moderating bird demography under droughts and compiled the data for these factors from published datasets. A meta-analysis is performed to determine the drought effect on bird demography at individual and population levels, accounting for the influence of species traits, timescale and severity of droughts, as well as biome features. The results show that droughts have an overall negative effect on bird demography, and the effect is mediated by different factors at each level. For individuals exposed to droughts, declines in demographic rates are found to be related to narrower extents of occurrence of species, and a significant overall reduction in demographic rates is identified for individuals residing in deserts and xeric shrublands. At the population level, declines in abundance or reproductive performance are generally identified for invertivores, frugivores, nectarivores and omnivores; short-lived species with small clutch sizes also show greater susceptibilities under the impacts of droughts. Our findings additionally suggest that the demographic vulnerability of bird individuals and populations could be affected by the duration and magnitude of drought episodes. Although our results are subject to publication bias, these conclusions advance the assessment of vulnerability to extreme climatic events that used to be based on equally weighted species traits and support bird conservation by prioritizing the declining populations of species with drought-susceptible traits.

Large invasive herbaceous plants decrease the taxonomic, functional and phylogenetic diversity of birds via their reproductive traits

Abstract Birds are among the organisms most impacted by plant invasions, the effects of which are particularly conspicuous during the breeding season. Birds can incorrectly assess the suitability of large, invasive hogweeds Heracleum sp. in south‐eastern Poland when selecting nesting sites early in spring when the developing invaders do not yet differ substantially in form from the rest of the vegetation. One would expect lower bird breeding success in areas with invasive hogweeds. Furthermore, this may shift bird community composition towards species with filtered traits, which may then be reflected in various measures of diversity. To assess these expectations, we conducted bird surveys at 74 sites, arranged as 37 pairs (with invasive Heracleum vs. control). The presence of Heracleum was associated with lower bird taxonomic and phylogenetic diversity. Functional richness (calculated based on species' reproductive traits) was also lower at sites with these invaders. The species detected at Heracleum sites were characterised by traits associated with rapid breeding, for example, small clutches, short incubation periods and short fledging periods. We show that the bird community at sites with hogweeds became less diverse and composed of random species sharing similar reproductive traits. Bird communities with low diversity at Heracleum sites tended to exhibit a common trait syndrome. These patterns provide insights into the mechanisms of how invasive plants may lead to the loss of some traits and species in bird communities. Read the free Plain Language Summary for this article on the Journal blog.

The effect of experimental warming on reproductive performance and parental care in the burying beetle Nicrophorus nepalensis.

Rising temperatures can adversely affect parental care and reproductive performance across a range of taxa. However, the warming impact is contingent upon understanding how temperature affects the spectrum of parental behaviours and their interplay. Here, we assessed how temperature affects parental care and reproductive success in the burying beetle, Nicrophorus nepalensis, which exhibits complex parental care behaviours. We exposed breeding pairs of N. nepalensis, to three temperature regimes (18°C, 20°C and 22°C) and assessed changes in parental care, and the subsequent development and growth of their offspring. Our findings show that 22°C disrupts carcass nest building by the parents and results in smaller clutches. Moreover, no eggs successfully hatched in the 22°C treatment. A milder increase to 20°C did not affect the hatching rate but resulted in smaller broods and lighter offspring, even when considering brood size, suggesting a change in post-hatching care quality. Our research suggests that warming may weakly affect parental care but has strong detrimental effects on offspring performance. These findings highlight the necessity of investigating the effect of ambient temperature across a diversity of traits and behaviours and across a range of life-history stages to fully assess species vulnerability in the face of future climate change.

Divergent Importance and Geographic Patterns in Threats to Birds and Mammals in China

ABSTRACTAimWildlife populations are continuing to decrease worldwide. Understanding the ranking and distribution of drivers of species declines is crucial to enable targeted actions to counteract major threats. However, few studies have assessed the relative importance and geographic distribution of threats to biodiversity in China, even for high‐profile groups such as birds and mammals. Therefore, this study aims to rank and map the distribution of threat to birds and mammals in China, which could provide novel insight into biodiversity conservation in China.LocationChina.MethodsA database of different threats for 147 threatened bird species and 176 threatened terrestrial mammal species was obtained from China's Red List of Biodiversity published in 2021. We collated information on the distribution and threat categories for birds and mammals in China, aiming to classify, rank and map threats. We used Bray–Curtis dissimilarity index to examine the correlations of threats occurring simultaneously, and compared the distribution of habitat of threatened birds and mammals. In addition, we conducted threat ranking analyses of threatened birds and mammals between different orders and traits (body mass and clutch/litter sizes).ResultsThe results showed that the most common threats to birds were habitat loss, hunting, human disturbance, agriculture, pollution and logging, while the most common threats to mammals were hunting, agriculture, logging, habitat loss, human disturbance and livestock farming or ranching. These threats showed different geographic patterns, and some threats frequently co‐occur as threat syndromes. Forests were the primary habitat for most threatened species, and orders formed by larger species with small clutch or litter sizes were more likely to be threatened.Main ConclusionsWe highlight the most common threats and key areas for conservation. Furthermore, focusing on clusters of co‐occurring threats may be the most effective way to aid recovery of threatened species, and targeted actions are needed to counter ongoing population declines in many groups. These actions should not be limited to the protection of regions where species are at risk of multiple significant threats, but should also include the maintenance and restoration of native forests and strategic planning of afforestation through planted forests.

Environmental constraints can explain clutch size differences between urban and forest blue tits: Insights from an egg removal experiment.

Urban environments present novel ecological challenges to wild species. In birds, urban populations generally exhibit reduced clutch sizes compared to forest populations. However, whether smaller urban clutches are adaptive or a result of environmental constraints is unclear. To investigate these two hypotheses, we quantified the ability of urban and non-urban blue tits (Cyanistes caeruleus) to lay new eggs after an experimental manipulation aimed to increase egg production. We removed the first four eggs laid by urban and forest birds to test their ability to produce new eggs. If the urban environment imposes constraints on egg production, we predicted that urban birds would not lay new eggs. If the small clutches of urban birds are an adaptive response, we predicted they would lay new eggs to reach the optimal clutch size for the environment. Consistent with the environmental constraint hypothesis, our results suggest that urban females do not lay new eggs to the same extent as forest birds following egg removal. Forest birds laid approximately two new eggs after our experimental manipulation, while urban birds laid approximately 0.36 new eggs following egg removal. Our manipulation resulted in a brood reduction in the urban experimental nests, yet there was no difference in the number of fledged offspring between urban control and experimental nests. This suggests that females might be misjudging urban habitat quality and produce a clutch with more eggs than nestlings they can rear. Overall, our results suggest that environmental constraints could limit the number of eggs that urban females lay, generating urban versus non-urban differences in this trait.

The effects of land use changes on site occupancy and breeding success of the barn owl (Tyto alba) from 1993 to 2020

Land use changes, driven by human activities such as agricultural intensification and urban expansion, have drastic effects on biodiversity. As these changes are anticipated to continue, understanding species’ adaptations to their evolving habitats is essential to find solutions for effective conservation efforts and sustainable management. In this study, we investigated how long-term changes in the agricultural landscape influence the breeding performance of a population of barn owls (Tyto alba) residing in nest boxes using data collected from 1993 until 2020. Specifically, we assessed how agricultural intensification, urbanization, and site availability affected barn owls' site occupancy and breeding success. Our results reveal that nest boxes surrounded by more agricultural fields are more likely to be occupied and have higher fledging success. Additionally, nest boxes installed higher on the barn were more likely to be occupied. Owls laid more eggs in nest boxes facing North than South or East. Clutches laid in nest boxes installed at higher altitudes were smaller. Finally, nest boxes with a higher density of surrounding nest boxes were less likely to be occupied and had smaller clutches. These insights show barn owls high reliance on the agricultural landscape surrounding their nesting sites, but also the importance of nest box characteristics to optimize their breeding success.

Bird specimen number linked with species trait and climate niche breadth

Biological specimens are fundamental for taxonomy and flora/fauna research. More importantly, they also play crucial roles in recording environmental impacts on morphology and behavior, which is vital for biodiversity research and conservation. However, there are few systematic studies on the patterns and drivers of bird specimen number at regional scales. This study is the first attempt to examine the relationships between bird specimen number and species traits as well as climate niche breadth in China, aiming to answer two questions: 1) how do species’ temperature niche breadth and precipitation niche breadth influence specimen number? 2) which trait is most associated with bird specimen number? The associations between bird specimen number and explanatory variables were examined using ordinary least squares, generalized linear models, phylogenetic generalized linear mixed models, and multiple comparisons. The results showed that Muscicapidae was the family with the highest specimen number, and Passeriformes was the order with the highest specimen number. Bird specimen number significantly increased with larger temperature niche breadth and precipitation niche breadth. Specimen number was also positively associated with geographic range size, habitat specificity, hunting vulnerability and clutch size, but negatively associated with body size. These findings suggest that future bird specimen collection should pay more attention to birds with limited ecological niches, large body sizes, and small clutch sizes. This research enhances the use of bird specimen data to study and preserve biodiversity.

Life history traits and cancer prevalence in birds.

Cancer is a disease that affects nearly all multicellular life, including the broad and diverse taxa of Aves. While little is known about the factors that contribute to cancer risk across Aves, life history trade-offs may explain some of this variability in cancer prevalence. We predict birds with high investment in reproduction may have a higher likelihood of developing cancer. In this study, we tested whether life history traits are associated with cancer prevalence in 108 species of birds. We obtained life history data from published databases and cancer data from 5,729 necropsies from 108 species of birds across 24 taxonomic orders from 25 different zoological facilities. We performed phylogenetically controlled regression analyses between adult body mass, lifespan, incubation length, clutch size, sexually dimorphic traits, and both neoplasia and malignancy prevalence. We also compared the neoplasia and malignancy prevalence of female and male birds. Providing support for a life history trade-off between somatic maintenance and reproduction, we found a positive relationship between clutch size and cancer prevalence across Aves. There was no significant association with body mass, lifespan, incubation length, sexual dimorphism, and cancer. Life history theory presents an important framework for understanding differences in cancer defenses across various species. These results suggest a trade-off between reproduction and somatic maintenance, where Aves with small clutch sizes get less cancer.

Variation in reproductive success in a fragmented Meadow Pipit population: a role for vegetation succession?

Most farmland birds experience strong declines across Europe. These declines are typically associated with agricultural intensification but research on alternative local causes remains scarce. We investigated variation in reproductive success as a potential driver for the observed population declines in a fragmented population of the Meadow Pipit Anthus pratensis, a representative inhabitant of extensively managed mountain grasslands across Europe. Intense nest surveys in the entire Meadow Pipit metapopulation of the Northern Black Forest (SW Germany) between 2020 and 2022 provided information on reproductive success for 53 females distributed across nine habitat patches along an 18 km ridge of the Northern Black Forest. Hatching dates delayed by approx. 5.0 days per 100 m altitude and were almost 10 days later in a year with cold and rainy spring weather. Mean reproductive success per female and year (3.45 fledglings) was low compared to literature values (approx. 4.5) and may thus drive ongoing population declines. Mayfield nest survival estimates (approx. 51% across the nesting period) were comparably high, with most nest failures linked with predation or adverse weather. Low reproductive success further associated with comparably small clutch sizes and low fractions of second broods in habitat patches characterized by homogeneously dense swards. We suggest that restoration through extensive permanent cattle grazing coupled with succession control may be a key factor to increase population productivity.

Genetic tools for the study of the mangrove killifish, Kryptolebias marmoratus, an emerging vertebrate model for phenotypic plasticity.

Kryptolebias marmoratus (Kmar), a teleost fish of the order Cyprinodontiformes, has a suite of unique phenotypes and behaviors not observed in other fishes. Many of these phenotypes are discrete and highly plastic-varying over time within an individual, and in some cases reversible. Kmar and its interfertile sister species, K. hermaphroditus, are the only known self-fertile vertebrates. This unusual sexual mode has the potential to provide unique insights into the regulation of vertebrate sexual development, and also lends itself to genetics. Kmar is easily adapted to the lab and requires little maintenance. However, its internal fertilization and small clutch size limits its experimental use. To support Kmar as a genetic model, we compared alternative husbandry techniques to maximize recovery of early cleavage-stage embryos. We find that frequent egg collection enhances yield, and that protease treatment promotes the greatest hatching success. We completed a forward mutagenesis screen and recovered several mutant lines that serve as important tools for genetics in this model. Several will serve as useful viable recessive markers for marking crosses. Importantly, the mutant kissylips lays embryos at twice the rate of wild-type. Combining frequent egg collection with the kissylips mutant background allows for a substantial enhancement of early embryo yield. These improvements were sufficient to allow experimental analysis of early development and the successful mono- and bi-allelic targeted knockout of an endogenous tyrosinase gene with CRISPR/Cas9 nucleases. Collectively, these tools will facilitate modern developmental genetics in this fascinating fish, leading to future insights into the regulation of plasticity.

Variations in the Reproductive Strategies of Different Charadrius alexandrinus Populations in Xinjiang, China.

Due to the influence of bio-geographical and environmental factors, as well as anthropogenic landscape features, organisms show different reproductive strategies among different populations. There is a lack of detailed information on the reproductive biology of Kentish plover Charadrius alexandrinus in arid lands in Central Asia. In this study, we summarized the characteristics of the reproductive biology of three geographically distinct plover populations in Aibi Lake in northwestern Xinjiang, Taitema Lake in southern Xinjiang and artificial reservoirs around Urumqi City in northern Xinjiang, based on 440 eggs from 158 nests observed and analyzed from April to July of 2019 and 2020. We found that there was no significant difference in clutch size among the three populations. However, the egg size of the Taitema Lake population was significantly larger than those of the other two populations, whilst the egg volume and clutch volume of the artificial reservoirs' populations were significantly larger than that of Aibi Lake. With the postponement of laying dates, the northern and northwestern populations showed the characteristics of a small clutch size and a relatively small egg size, respectively, and a decrease in reproductive output. The heavier female plovers in Taitema Lake laid eggs earlier, and there was a significantly positive correlation between female body mass and clutch size and egg size. The tarsometatarsus length of the female plovers was significantly positively correlated with the reproductive output in all three populations. The model selection results show that female body size and ambient temperature restrict the egg size and reproductive output of Kentish plovers, which is consistent with the upper limit hypothesis of the maternal condition and maternal constraint. Our data support the hypothesis that Kentish plovers show distinct flexibility in their breeding strategies to cope with the harsh natural environment in the arid lands of Xinjiang, China. The results of a relatively high average clutch size and average egg size imply that the saline wetlands of Western China are important breeding habitats for Kentish plovers.

Environmental seasonality and latitude drive clutch size diversity in female lizards across populations

Global patterns in clutch size variations across species have been linked to resource availability and seasonal climate change. However, our understanding of the specific local-scale drivers of clutch size diversity has remained unclear, especially among populations of ectotherms with relatively homogeneous genetic structures experiencing varying local environmental conditions. And understanding the specific local-scale drivers of clutch size diversity within species can provide insight into the local adaptation of species or the evolution of key life history traits. Here, we collected clutch size data of a wide-ranging female lizard (Eremias argus) from field observation and literature across populations of varying elevations and latitudes in China. We then used mixed-effects models to test the relationship between clutch size, body size, habitat type, elevation, latitudes, and climate conditions. Unsurprisingly, body size was positively correlated with clutch size variations across all populations. When we accounted for body size, females from populations at higher latitudes had larger clutches, while females in less variable rainfall environments had smaller clutches. Interestingly, we found that females occupying higher geographic gradients (e.g., latitude and elevation) with certain habitats (e.g., grasslands and farmlands) were associated with larger clutch sizes. Thus, our study shows support for similar global macroecological drivers of clutch size diversity among lizard species, and also suggests that female ectotherms might have different reproductive decisions employed in response to local climates to maximise population replacement.

Filial Cannibalism Leads to Chronic Nest Failure of Eastern Hellbender Salamanders (Cryptobranchus alleganiensis).

AbstractIn species that provide parental care, parents will sometimes cannibalize their own young (i.e., filial cannibalism). Here, we quantified the frequency of whole-clutch filial cannibalism in a species of giant salamander (eastern hellbender; Cryptobranchus alleganiensis) that has experienced precipitous population declines with unknown causes. We used underwater artificial nesting shelters deployed across a gradient of upstream forest cover to assess the fates of 182 nests at 10 sites over 8 years. We found strong evidence that nest failure rates increased at sites with low riparian forest cover in the upstream catchment. At several sites, reproductive failure was 100%, mainly due to cannibalism by the caring male. The high incidence of filial cannibalism at degraded sites was not explained by evolutionary hypotheses for filial cannibalism based on poor adult body condition or low reproductive value of small clutches. Instead, larger clutches at degraded sites were most vulnerable to cannibalism. We hypothesize that high frequencies of filial cannibalism of large clutches in areas with low forest cover could be related to changes in water chemistry or siltation that influence parental physiology or that reduce the viability of eggs. Importantly, our results identify chronic nest failure as a possible mechanism contributing to population declines and observed geriatric age structure in this imperiled species.

Reproduction of the Western Marsh Harrier Circus aeruginosus at the El Maleh Dam reservoir in north-western Morocco

The reproduction of the Western Marsh Harrier Circus aeruginosus in submerged and dried up thickets of French tamarisk Tamarix gallica at El Maleh Dam reservoir, Benslimane Province, Morocco, was studied through monitoring nests in three successive years (2017–2019). Systematic field investigation showed that the nests were concentrated exclusively in a narrow and shallow area upstream of the dam. The abundance of tamarisk is a determining factor in the breeding success of the Western Marsh Harrier at this site, by supporting the nests and giving them some protection from predation while the birds are close to agricultural fields, a favourable hunting ground. A study of individual broods revealed a relatively small clutch size (3.5 eggs per nest) and that incubation took 32 days on average. Compared with previous reports for this species elsewhere, the chicks fledged relatively early (33 or 35 days), but with a low fledgling success rate not exceeding 33.9%. The low fledgling success is partly attributable to the structure of the habitat, as the dense dry vegetation above the water level limits the movement of chicks out of nests yet favours the drowning of those that fall from the nest. Breeding success is influenced by a reduction in hunting territory caused by drops in the water level during periods of drought, poor climate conditions, and disturbance caused by human activities in the reservoir lake and riparian farmland. In addition to these environmental factors, nest failure due to nest destruction is related to the experience of the pairs in choosing the nesting site and their ability to weave the nest-building materials. Further study is needed on the characteristics of this highly specific habitat and its state of conservation, the reproduction of coexisting bird populations, and human activities around the breeding site.

한려해상국립공원 홍도와 태안 난도의 괭이갈매기 번식현황

Seabirds take a long time to recover if their population decreases due to slow growth and small clutch size. This study was conducted to collect basic data of breeding status of Black-tailed gulls (Larus crassirostris) on Hongdo Island of Hallyeohaesang National Park and and Nando Island. These two breeding colonies are designated as natural monuments. We investigated egg volume, clutch size and nest density in May 2022. As results, clutch size was 1.89±0.57 in Hongdo Island and 1.91±0.48 in Nando Island. The egg volume was also similar between Hongdo Island (59.22±5.47) and Nando Island (59.63±3.96). The nest density was significantly higher in Hongdo Island (1.27±0.18/㎡) than in Nando Island(0.54±0.15/㎡). Breeding population was estimated as 56,729 pairs in Hongdo Island while 14,112 pairs in Nando Island based on the proportion of breeding areas. Long-term monitoring is required to know the trends of Black-tailed gulls to protect breeding colonies.

The Survival Rate from Splitting Clutch Design Method for Green Turtle's Relocated Nest in Penang Island, Malaysia.

Ten nests were collected from Kerachut and Teluk Kampi, Penang Island between 2 August 2009 and 9 December 2009, and each one nest was split into three small clutch sizes for incubation at three nesting depths (45 cm, 55 cm and 65 cm), with a total of 30 modified nests for this experiment. Three important objectives were formulated; to observe on the survival hatchings among the three nesting depths, to study on the effects of sand temperature on incubation period among the three nesting depths, and to investigate the influence of sand temperature on hatchling's morphology. Main result shows that the mean survival of the hatchlings was 25.40% at 45 cm nesting depth, followed by mean 17.60% at 55 cm nesting depth, and lastly, the mean was 21.50% at 65 cm nesting depth. Overall, there are 56.63% survival hatchlings, 10.97% dead hatchlings and 32.40% unhatched eggs were produced. The incubation period was also found to be significantly correlated with sand temperature, p > 0.001, and nesting depth, p < 0.001. The hatchling's length and weight varies is sizes across the nesting depths, p < 0.001. However, the small difference in hatchling sizes per nesting depths are not strong enough to prove the significant correlation with sand temperature, p > 0.05. This article provides a basic knowledge from the splitting clutch design method. A sum of 50%-60% survivals hatchlings produced were incubating under small range of clutch sizes, 29 to 49 eggs. This article provides basic result on the survival hatchlings, eggs survivorship, incubation period, temperature, hatchling's morphology and discussion on implication of this method on conservation in Malaysia.

Effect of extreme weather on the breeding parameters of great tits Parus major: comparison of two very different seasons

Climate change and extreme weather events may be seen as an opportunity to help understand the mechanisms by which birds adjust their breeding parameters to environmental variability. In the breeding season of 2020, several factors, such as a prolonged drought period, a relatively warm winter with no snow cover, and a cold spring (the coldest May in Poland since 1991) affected many bird populations in Poland. The great tit Parus major tended to produce much smaller clutches, much fewer fledglings, and had very low breeding success, increasing with the progress of the breeding season in 2020, in contrast to the more typical breeding season characterised by average weather parameters in 2018. In light of the results obtained, we agree with the view that the phenotypic plasticity of the breeding parameters of the studied birds, such as phenology, may be insufficient to adjust to the upcoming extreme weather events. Additionally, further examining of the impact of extreme weather events on the breeding biology of animals is an important goal for future studies.

High MHC diversity confers no advantage for phenotypic quality and reproductive performance in a wild bird.

Genes of the major histocompatibility complex (MHC) encode antigen‐binding molecules and are an integral part of the acquired immune response of vertebrates. In general, high individual MHC diversity is expected to increase fitness by broadening the spectrum of pathogens recognized by the immune system, in accordance with the heterozygote advantage mechanism. On the other hand, the optimality hypothesis assumes that individuals with optimal (intermediate), rather than maximum, diversity of the MHC will achieve the highest fitness because of inherent costs associated with expressing diverse MHC alleles.Here, we tested for associations between individual diversity of the MHC class I and class II genes (binding antigens of intra‐ and extracellular pathogens respectively) and a range of fitness‐related traits (condition, ornament expression and reproduction) in an urban population of the Eurasian coot Fulica atra.Contrary to our expectation, we found that high within‐individual allelic diversity of MHC genes (both class I and II) was associated with poorer condition (lower blood haemoglobin concentrations), weaker expression of the putative ornament (smaller frontal shield), later onset of breeding and smaller clutches. An analysis of functional MHC allele clusters (supertypes) provided further support for negative associations of MHC diversity with phenotypic quality and reproductive performance, but most of these relationships could not be explained by the presence of specific maladaptive supertypes. Finally, we found little empirical support for the optimality hypothesis in the Eurasian coot.Our results suggest that the costs of high MHC diversity outweighed any benefits associated with broad MHC repertoire, which could be driven by depauperate pathogen diversity in an urban landscape. To the best of our knowledge, this is one of the first studies providing consistent evidence for negative associations of MHC diversity with a range of fitness‐related traits in a natural avian population.

The Immunological and Oxidative Costs of Reproduction and Associations between Maternal and Egg Yolk Physiology in a Reptile

Energetic constraints caused by reproductive investment may incur immunological and oxidative costs to a female and potentially to her developing offspring. Oviparous reptiles are capable of altering offspring phenotype through differential allocation of physiological factors during vitellogenesis (yolk formation), depending upon the external environment and the physiological state of the female. Despite its importance in protecting developing offspring against infection, maternal transfer of immune factors has rarely been studied in reptiles. Furthermore, the extent to which offspring may be impacted by the inherent oxidative costs of vitellogenesis is not well understood. Using the Side-blotched Lizard (Uta stansburiana) as a model, we examined how reproductive investment (clutch size and mass) influenced maternal immunological (BKA) and oxidative state (ROMs) and whether these metrics covaried with egg yolk immunity and oxidative state. We assessed factors influencing variation in egg yolk BKA and ROMs within and across clutches from all females and found that females with smaller clutches had higher BKA and ROMs than females with larger clutches. There was also an overall positive relationship between maternal BKA and ROMs and clutch mass, regardless of clutch size. We did not find maternal and egg yolk BKA and ROMs to be directly related, but yolk ROMs decreased as egg mass increased. Within-clutch variation in yolk BKA and ROMs was not related to maternal investment, but variation among clutches was explained by maternal identity. Because egg yolk physiology can impose long-lasting or permanent changes to offspring, these results create a foundation for future work investigating factors contributing to yolk physiology and highlight the necessity of considering multiple physiological and ecological variables when conducting eco-immunological research.