Ovarian dynamics, egg size, and egg number in relation to temperature and mating status in a butterfly

Although the temperature‐size rule, that is, an increase in egg (and body) size at lower temperatures, applies almost universally to ectotherms, the developmental mechanisms underlying this consistent pattern of phenotypic plasticity are hitherto unknown. By investigating ovarian dynamics and reproductive output in the tropical butterfly Bicyclus anynana (Butler) (Lepidoptera: Nymphalidae: Satyrinae) in relation to oviposition temperature and mating status, we tested the relevance of several competing hypotheses for temperature‐mediated variation in egg size and number. As expected, females ovipositing at a lower temperature laid fewer but larger eggs than those ovipositing at a higher temperature. Despite pronounced differences in egg‐laying rates, oocyte numbers were equal across temperatures at any given time, while oocyte size increased at the lower temperature. In contrast, there were greatly reduced oocyte numbers in mated compared to virgin females. Our results indicated that temperature‐mediated plasticity in egg size cannot be explained by reduced costs of somatic maintenance at lower temperatures, enabling the allocation of more resources to reproduction (reproductive investment was higher at the higher temperature). Furthermore, there was no indication for delayed oviposition (no accumulation of oocytes at the lower temperature, in contrast to virgin females). Rather, low temperatures greatly reduced the oocyte production (i.e., differentiation) rate and prolonged egg‐maturation time, causing low egg‐laying rates. Our data thus suggested that oocyte growth is less sensitive to temperature than oocyte production, resulting in a lower number of larger eggs at lower temperatures.     

Field and experimental evidence for competition's role in phenotypic divergence

Resource competition has long been viewed as a major cause of phenotypic divergence within and between species. Theory predicts that divergence arises because natural selection favors individuals that are phenotypically dissimilar from their competitors. Yet, there are few conclusive tests of this key prediction. Drawing on data from both natural populations and a controlled experiment, this paper presents such a test in tadpoles of two species of spadefoot toads (Spea bombifrons and S. multiplicata). These two species show exaggerated divergence in trophic morphology where they are found together (mixed-species ponds) but not where each is found alone (pure-species ponds), suggesting that they have undergone ecological character displacement. Moreover, in pure-species ponds, both species exhibit resource polymorphism. Using body size as a proxy for fitness, we found that in pure-species ponds disruptive selection favors extreme trophic phenotypes in both species, suggesting that intraspecific competition for food promotes resource polymorphism. In mixed-species ponds, by contrast, we found that trophic morphology was subject to stabilizing selection in S. multiplicata and directional selection in S. bombifrons. A controlled experiment revealed that the more similar an S. multiplicata was to its S. bombifrons tankmate in resource use, the worse was its performance. These results indicate that S. multiplicata individuals that differ from S. bombifrons would be selectively favored in competition. Our data therefore demonstrate how resource competition between phenotypically similar individuals can drive divergence between them. Moreover, our results indicate that how competition contributes to such divergence may be influenced not only by the degree to which competitors overlap in resource use, but also by the abundance and quality of resources. Finally, our finding that competitively mediated disruptive selection may promote resource polymorphism has potentially important implications for understanding how populations evolve in response to heterospecific competitors. In particular, once a population evolves resource polymorphism, it may be more prone to undergo ecological character displacement.     

Phenological mismatch drives selection on elevation,but not on slope,of breeding time plasticity in a wild songbird

Phenotypic plasticity is an important mechanism for populations to respond to fluctuating environments, yet may be insufficient to adapt to a directionally changing environment. To study whether plasticity can evolve under current climate change, we quantified selection and genetic variation in both the elevation (RN_E) and slope (RN_S) of the breeding time reaction norm in a long‐term (1973–2016) study population of great tits (Parus major). The optimal RN_E (the caterpillar biomass peak date regressed against the temperature used as cue by great tits) changed over time, whereas the optimal RN_S did not. Concordantly, we found strong directional selection on RN_E, but not RN_S, of egg‐laying date in the second third of the study period; this selection subsequently waned, potentially due to increased between‐year variability in optimal laying dates. We found individual and additive genetic variation in RN_E but, contrary to previous studies on our population, not in RN_S. The predicted and observed evolutionary change in RN_E was, however, marginal, due to low heritability and the sex limitation of laying date. We conclude that adaptation to climate change can only occur via micro‐evolution of RN_E, but this will necessarily be slow and potentially hampered by increased variability in phenotypic optima.     

Phenotypic integration between claw and toepad traits promotes microhabitat specialization in the Anolis adaptive radiation

The performance of an organism in its environment frequently depends more on its composite phenotype than on individual phenotypic traits. Thus, understanding environmental adaptation requires investigating patterns of covariation across functionally related traits. The replicated adaptive radiations of Greater Antillean Anolis lizards are characterized by ecological and morphological convergence, thus, providing an opportunity to examine the role of multiple phenotypes in microhabitat adaptation. Here, we examine integrated claw and toepad morphological evolution in relation to habitat partitioning across the adaptive radiations of Greater Antillean anoles. Based on analysis of 428 specimens from 57 species, we found that different aspects of claw morphology were associated with different perch dimensions, with claw height positively associated with perch diameter and claw curvature positively associated with perch height. Patterns of integration also varied across claw and toepad traits, likely driven by correlative selection for performance on smoother and rougher substrates. Finally, rates of evolution differed between claw and toepad traits, with claw length evolving faster than all other traits despite having no predicted functional importance. Our results highlight the multivariate nature of phenotypic adaptation and suggest that phenotypic integration across Greater Antillean anoles is driven by fine‐scale correlative selection based on structural habitat specialization.     

Social runaway: Fisherian elaboration (or reduction) of socially selected traits via indirect genetic effects

Our understanding of the evolutionary stability of socially selected traits is dominated by sexual selection models originating with R. A. Fisher, in which genetic covariance arising through assortative mating can trigger exponential, runaway trait evolution. To examine whether nonreproductive, socially selected traits experience similar dynamics—social runaway—when assortative mating does not automatically generate a covariance, we modeled the evolution of socially selected badge and donation phenotypes incorporating indirect genetic effects (IGEs) arising from the social environment. We establish a social runaway criterion based on the interaction coefficient, ψ , which describes social effects on badge and donation traits. Our models make several predictions. (1) IGEs can drive the original evolution of altruistic interactions that depend on receiver badges. (2) Donation traits are more likely to be susceptible to IGEs than badge traits. (3) Runaway dynamics in nonsexual, social contexts can occur in the absence of a genetic covariance. (4) Traits elaborated by social runaway are more likely to involve reciprocal, but nonsymmetrical, social plasticity. Models incorporating plasticity to the social environment via IGEs illustrate conditions favoring social runaway, describe a mechanism underlying the origins of costly traits, such as altruism, and support a fundamental role for phenotypic plasticity in rapid social evolution.     

Signals of local adaptation across an environmental gradient among highly connected populations of the Dead Sea Sparrow Passer moabiticus in Israel

Populations found at the edge of a species range often have decreased genetic diversity, which together with high gene flow may reduce the ability of a species to adapt to local environmental conditions. The Dead Sea Sparrow Passer moabiticus occupies a disjointed range, where the Israeli populations are considered peripheral and fragmented. The species is also thought to have undergone a recent range expansion. We aimed to describe the genetic and morphological variation of the Israeli populations and to determine the extent of gene flow among them. We expected that because of the small latitudinal gradient across Israel and the recent range expansion of the species that Dead Sea Sparrow populations would show no significant morphological adaptation to local environmental conditions, and that considerable gene flow would be taking place among populations. Our findings indicate the existence of gene flow, suggesting high connectivity among populations, but recovered no support for a recent range expansion, possibly due to insufficient time since expansion for mutations to have accumulated. However, despite recurrent gene flow among populations, latitudinal variation in wing length (male and female) and body mass (male) was indicative of local adaptation across Israel, in accordance with Bergmann's rule.     

Plumage coloration and personality in early life: sexual differences in signalling

Several studies have shown that melanin‐based traits play a crucial role in social contexts as they are associated with dominance, personality and social behaviour. However, most of these studies have focused on adults, and the role of these traits in juveniles has rarely been explored. Here, we explore the association between two melanin‐based traits and nestling personality in Common Kestrels Falco tinnunculus. Our results show that female nestlings with blacker plumages displayed bolder personalities, providing evidence of sex‐dependent phenotypic integration of these two traits in males and females. We consider that this differential integration may arise from different selection pressures acting on males and females on plumage coloration during adulthood and that nestling coloration can act as a status signal within the juvenile age‐class.     

Central–periphery gradient of individual quality within a colony of Black‐headed Gulls

Central nesting sites within avian colonies are often more profitable in terms of fitness, as they can offer better protection against predators compared with colony edges. Thus, central sites are expected to attract high‐quality individuals, which should produce a clear central–periphery gradient in the phenotypic quality of nesting individuals and reproductive output within colonies. The aim of this study was to assess spatial patterns of individual quality within a colony of a common larid, the Black‐headed Gull Chroicocephalus ridibundus. We found that laying was advanced in the central zone of the colony when compared with the periphery, and central pairs tended to lay larger eggs and had higher hatching success than peripheral pairs. Centrally nesting individuals had higher blood haemoglobin concentrations, size‐corrected body mass and heterozygosity (males only), indicating their better condition and higher genetic quality. In contrast, central females had lower plasma albumin concentration, which could possibly be attributed to their greater investment in egg production. Finally, pairs breeding in the central zone of the colony had an elevated heterophil/lymphocyte ratio, suggesting that social stress can be recognized as an important cost of nesting in dense aggregations. The results provide empirical support for central–periphery gradients in the individual quality of colonially nesting Black‐headed Gulls, indicating that spatial gradients in pair quality should be carefully taken into account when conducting research on colonial birds.     

Expression profile of circular RNA in rat intimal hyperplasia and target gene prediction

Intimal hyperplasia is an important cause of stenosis or occlusion after vascular injury. Circular RNAs (circRNAs) are known to be related to various cardiovascular diseases. However, the expression profile of circRNAs in the neointima has not been reported in detail. In this study, we established a rat common carotid artery (CCA) injury model. A microarray detection showed significant differences in circRNA expression between the normal and injured CCA. Real-time quantitative polymerase chain reaction verified the differences. We used bioinformatics to predict the microRNAs that possibly interact with the differentially expressed (DE) circRNAs and linked the potential functions of circRNAs to the target genes of the microRNAs. We believe that the DE circRNA in neointima may affect the differentiation, proliferation, and migration of vascular cells through a variety of target genes. The intervention or utilization of certain circRNAs should be a new method for preventing and treating intimal hyperplasia.     

Repeatable inter‐individual variation in the thermal sensitivity of metabolic rate

Assessing whether trait variations among individuals are consistent over time and among environmental conditions is crucial to understand evolutionary responses to new selective pressures such as climate change. According to the universal thermal dependence hypothesis, thermal sensitivity of metabolic rate should not vary strongly and consistently among organisms, implying limited evolutionary response for metabolic traits under climate change. However, this hypothesis has been rarely tested at an individual level, leaving a gap in our understanding of climate change impacts on metabolic responses and their potential evolution. Using the amphipod Gammarus fossarum, we investigated the variability and repeatability of individual metabolic thermal reaction norms over time. We found large variations in both the thermal sensitivity (i.e. slope) and expression level (i.e. intercept) of individual metabolic reaction norms. Moreover, differences among individuals were consistent over time, and therefore repeatable. Inter‐individual variations in body mass resulted in a high repeatability of metabolic expression level but had no significant effect on the repeatability of thermal sensitivity. Overall, our results highlight that inter‐individual variability and repeatability of thermal reaction norms can be substantial. We conclude that these consistent differences among individuals should not be overlooked when apprehending the ecological and evolutionary effects of climate change.