Does habitat disturbance promote geographical parthenogenesis in whiptail lizards? Abstract Sexual and asexual organisms often vary in their distribution and abundances among habitats. These patterns of “geographical parthenogenesis” can shed light on ecological conditions underlying the evolution of sex. Habitat disturbance is hypothesized to be a mechanism that generates geographical parthenogenesis. Parthenogens are predicted to be more prevalent in disturbed habitats than sexuals due to the greater colonizing ability of parthenogens and the tendency of parthenogens to avoid competition with sexuals in undisturbed habitat. We tested whether habitat disturbance (i.e., a rapid state transition between vegetation communities) causes geographical parthenogenesis in whiptail lizards in the Chihuahuan Desert of southern New Mexico. Non-experimental approaches have shown the parthenogenetic Aspidoscelis uniparens commonly occurs in habitat with a history of vegetation disturbance from shrub removal, whereas the sexual A. marmorata occurs more often in undisturbed shrubland habitat. We used a field experiment replicated across 16 sites to test whether the parthenogen A. uniparens and sexual A. marmorata differ in their response to vegetation disturbance from shrub removal. The sites were distributed across a broad region of southern New Mexico, and we used a paired design with each site including a shrub-removal treatment and a control on 9-ha plots. Using a co-abundance model that accounts for imperfect detection, we found the parthenogen A. uniparens and sexual A. marmorata both responded positively to disturbance, but only when the congener was rare. Our results are inconsistent with the idea that parthenogens exploit disturbed habitat to avoid competition with sexuals. In our study system, A. uniparens often dominates older disturbed sites, especially two decades or more after shrub removal. Collectively, these results indicate geographical parthenogenesis emerges from biotic interactions in heterogeneous landscapes that include disturbed habitats used by sexual and asexual species alike.

Ecological specialization under multidimensional trade-offs Abstract Although trade-offs are expected to play an essential role in shaping the diversity in a community, their effects remain relatively nebulous and notoriously difficult to assess. This is especially true when multiple trade-offs of different classes interact, a situation here designated by multidimensional trade-offs. When dealing with single trade-offs, some information can be predicted solely based on their curvature. Does this generalize to when dealing with multidimensional trade-offs? What happens if the trade-offs have opposing curvatures? To address these issues, we develop a resource-based model that encompasses multiple trade-offs mediated by the acquisition and processing of resources. Two distinct classes of trade-offs are assumed: (1) a trade-off among resource uptake rates, (2) a trade-off between the resource uptake rate and yield of the process of conversion of resource into energy. The model considers a spatially structured population of microbial organisms that grow on an arbitrary number of resources. These resources flow into the system at a constant rate and diffuse through the environment. The individuals can adopt a variety of strategies through mutation constrained by trade-offs, which renders the model adaptive. We assess population sizes and levels of ecological specialization. The analysis of the results reveals that when multidimensional trade-offs are considered the classical intuition stemming from single trade-offs does not hold. The outcome can depend significantly not only on the curvature of the trade-offs but also on resource availability.

Stable isotope signatures and the trophic diversification of akodontine rodents Abstract Stable isotope analyses are frequently used to study trophic interactions, diet, and community processes, but they have seldom been applied to investigate the trophic niche structure of entire clades. In this paper, we assess stable isotopes information in a phylogenetic context to evaluate trophic evolution across the phylogeny of a diversified group of Neotropical cricetid rodents. A total of 139 hair samples of 47 species of Akodontini rodents were collected from five museum mammal collections and submitted to stable isotope analyses for δ13C and δ15N values. The resulting isotopic values were compared among the four main clades within the tribe. The phylogenetic signal of isotope values was estimated using a phylogenetic tree of Akodontini. Our results corroborate previous impressions that, in general, akodontines include more animal matter in their diet than other Neotropical rodents, but the lack of information for some species precludes more specific inferences. Some species appear to have relatively restricted niches, but the large variance observed in other species may be related to dietary and habitat differences related to ecological factors throughout the distribution of wide-ranging species. We found low phylogenetic signal for δ13C and δ15N values, suggesting that different regions within the isotopic niche space were occupied independently many times throughout akodontine evolutionary history. The δ13C/δ15N bi-plot indicates that the four main lineages occupy the trophic niche space in similar ways, although differing in trophic diversity. Our results represent new ecological information and an approach that can be useful in studying the evolution of trophic niches, and highlight the importance of museum specimen-based research for evolutionary ecology studies.

A multivariate phylogenetic comparative method incorporating a flexible function between discrete and continuous traits Abstract One major challenge of using the phylogenetic comparative method (PCM) is the analysis of the evolution of interrelated continuous and discrete traits in a single multivariate statistical framework. In addition, more intricate parameters such as branch-specific directional selection have rarely been integrated into such multivariate PCM frameworks. Here, originally motivated to analyze the complex evolutionary trajectories of group size (continuous variable) and social systems (discrete variable) in African subterranean rodents, we develop a flexible approach using approximate Bayesian computation (ABC). Specifically, our multivariate ABC-PCM method allows the user to flexibly model an underlying latent evolutionary function between continuous and discrete traits. The ABC-PCM also simultaneously incorporates complex evolutionary parameters such as branch-specific selection. This study highlights the flexibility of ABC-PCMs in analyzing the evolution of phenotypic traits interrelated in a complex manner.

Artificial seed aging reveals the invisible fraction: Implications for evolution experiments using the resurrection approach Abstract Non-random mortality is a key driver of evolution, but mortality that occurs early in life leaves adult traits of individuals that died unknown. This can lead to the invisible fraction problem, which causes difficulty in measuring selection and evolution in natural and experimental populations. Furthermore, seeds or other propagules that are stored intentionally or that persist in dormant states in nature can experience storage conditions that alter adult traits. Invisible fraction and storage condition effects can cause bias in evolutionary studies such as those using the resurrection approach of comparing ancestors and descendants in common environments. To investigate invisible fraction and storage condition effects, we subjected seeds of Brassica rapa Fast Plants to artificial aging under hot, humid conditions. We grew plants from artificially aged seeds alongside unaged control seeds for two generations and measured morphological and phenological traits on adult plants. We found that the plants from artificially aged seeds flowered later than those from unaged seeds in both the first and second generation, indicating storage condition and invisible fraction biases. However, the difference in flowering time was smaller in the second generation, indicating that the refresher generation decreased the storage condition effect. We also found that seeds that survived artificial aging were smaller than seeds that did not survive, indicating a potential physical basis for non-random mortality in storage. These results suggest that invisible fraction and storage condition effects can bias the results of resurrection experiments, and that the proper storage of seeds for use in resurrection experiments, as well as a refresher generation, are critical for valid results. The results also demonstrate that artificial aging can be used as a tool for studying mortality of propagules in nature, such as in soil seed banks, thus providing insight into evolutionary processes that would otherwise remain obscure.

Discovery and description of a novel sexual weapon in the world’s most widely-studied freshwater turtle Abstract Sexually coercive reproductive tactics are widespread among animals, where one sex employs specialized structures, called sexual weapons, to harass, intimidate, and/or physically force the other sex to mate. Painted turtles (Chrysemys picta) have been extremely well-studied over the last two centuries, and their mating system has been described as female choice based on male courtship display. The present study arises from observation that males seemingly have more protracted and serrated anterior marginal scutes than females. We hypothesized that the anterior carapace is sexually dimorphic, and that this morphology is a weapon used by males in coercive mating. We quantified anterior carapacial morphology using geometric morphometric analysis of digital photographs, drawing on samples of painted turtles from North American museum collections and our field site in Algonquin Provincial Park. We found that the anterior carapace of males had a significantly more serrated and projected shape compared to females, consistent with the sexual weapon hypothesis. Additionally, anterior carapacial shape was more strongly related to body size in males. Behavioural field observations strongly suggest that males use this morphology as a weapon to harm females during reproduction. The present study complements and strengthens the recent hypothesis that male painted turtles engage in coercion as an alternative reproductive tactic, questioning the long-understood paradigm of exclusive female choice in this well-studied species. Our study invites new avenues of research on the evolution of female harm in a system with extreme selection on female longevity and for which operational sex ratios vary among populations. Further, our work underlines how basic natural history observations can transform our understanding of well-studied systems.

Fitness costs of the cultivable symbiont Serratia symbiotica and its phenotypic consequences to aphids in presence of environmental stressors Abstract Associations between symbiotic microorganisms and animals are ubiquitous and hosts may benefit from hosting microbial communities through enhanced protection to environmental stresses or resource exploitation. Like many insects, aphids are hosts of a wide diversity of heritable symbionts that can be important drivers of their evolutionary ecology. Serratia symbiotica is one of the most common symbiont associated with aphids and includes a great variety of strains whose degree of interdependence on hosts varies significantly. Among these strains, some are gut-associated and have been isolated from aphids and cultivated. One of these strains (CWBI-2.3T) confers immediate protection against parasitoids. Here, we investigated additional associated phenotypes to elucidate the implication of cultivable S. symbiotica in the aphid evolutionary ecology. We show that under benign conditions, the aphids tended to suffer from reduced survival and fecundity when harboring the symbiont. We also demonstrate that gut infection with cultivable S. symbiotica does not protect aphids from the fungal pathogen Zoophtora occidentalis and from the lethal pathogen Serratia marcescens. However, while the bacterium is costly for aphids, this effect is no longer observed in the presence of the fungus, suggesting a negative effect of S. symbiotica on the latter. Our results further demonstrate that the cultivable S. symbiotica strain does not confer benefits to its hosts after the aphids were heat-stressed. These findings exposed that cultivable S. symbiotica does not have the same fitness effects on aphids as endosymbiotic strains, highlighting the significance of considering intraspecific variation of symbionts when studying their associated extended phenotypes.

Close encounters of the urban kind: predators influence prey body size variation in an urban landscape Abstract Body size is a key trait linked to many aspects of an organism’s life history, physiology, and behavior. Variation in body size can thus have important fitness consequences across a broad range of ecological contexts. We utilized the variation in multiple abiotic and biotic factors found among urban habitats to test simultaneously their relative effects on body size variation in urban populations of brown anole lizards (Anolis sagrei). These factors represent major hypotheses regarding body size variation in ectotherms and other animal groups: temperature, food availability, conspecific abundance and predator abundance. We also performed a tethered intruder experiment to determine whether the attack behavior of predatory curly-tailed lizards (Leiocephalus carinatus) depends on the body size of their brown anole prey. Lastly, we conducted a common garden experiment to assess whether brown anole body size differences between sites with and without curly-tailed lizard predators are genetically based. Predator abundance was the primary predictor of brown anole body size for both males and females. No other hypotheses were consistently supported. Brown anole body size increased along with increasing predator abundance, and predator abundance was negatively related to body size variation. Additionally, predators approached larger brown anoles less often and at longer latencies compared to smaller ones. Finally, male brown anoles from sites with predators had faster growth rates compared to those from sites without predators under common conditions in the lab. Brown anole body size differences among populations may result from higher survival of larger lizards during predatory confrontations, and this trait is at least partially heritable in males. Therefore, our results suggest that curly-tailed lizard predators may be important agents of evolution by natural selection for brown anole populations in urban habitats. To further investigate the ecological and evolutionary consequences of predator–prey interactions in urban habitats, future research should focus on measuring predator-induced selection in these novel environments.

Pheomelanin-based coloration is related to individual quality and oxidative stress in blue petrels Abstract In several species, the rusty color of hair or feathers is due to pheomelanin pigments, whose adaptive function is unknown. Pheomelanin may be costly because it is phototoxic and its production consumes a key intracellular antioxidant. Pheomelanin-based traits are, however, positively associated with individual quality in several bird species, where they have thus been suggested to have evolved through sexual selection. Here we investigated the signaling potential of the pheomelanin-based coloration of the crown feathers in the blue petrel. Although this pelagic seabird is nocturnal at the breeding colony and breeds within deep burrows, it might use visual communication when settled on the water during daytime. We tested the correlation between crown color and several fitness-related traits, and we found that higher-quality females displayed less-orange crown than poorer-quality females. This result is inconsistent with an adaptive function of pheomelanin-based coloration in inter-, or intra-, sexual selection in females. We suggest that it might, however, be in line with a signaling function of eumelanin-based coloration, if inter-individual variations in orange coloration are mainly due to eumelanin-to-pheomelanin ratio, rather than to pheomelanin quantity. In contrast to females, we did not find strong evidence for associations between melanin-based coloration and individual quality in males, suggesting sex-specific selective pressures on melanin-based traits in this species.

From sympatry to parapatry: a rapid change in the spatial context of incipient allochronic speciation Abstract Speciation is nowadays recognized as a dynamic process in which the respective roles of forces driving ecological differentiation and reproductive isolation can change through time and space. Incipient speciation events are particularly useful to follow such processes that are not tractable when considering well-differentiated taxa. A promising case study was discovered in the pine processionary moth, Thaumetopoea pityocampa, a Mediterranean defoliator of Pinus species, for which allochrony acting as an automatic magic trait was recognized as the major driver of an incipient speciation process. In Portugal, a unique population with a shifted phenology, known as the summer population (SP), co-occurs with a population following the typical life cycle, known as the winter population (WP). We monitored male activity of both populations in the Leiria region, i.e. over the whole SP distribution range using a systematic sampling along two transects, and studied Portuguese WPs at a larger geographical scale to explore their genetic diversity and spatial pattern of differentiation. Results showed that the WPs were genetically more diverse than the SP, with a strong pattern of isolation by distance both at large and small spatial scales, while the SP was very homogeneous over its whole range, without signature of its recent spatial expansion. Contrary to our expectations, no F1 hybrids were identified, even though we found an extended flight period of the SP, overlapping with the beginning of the WP reproductive period. Interestingly, the SP was found to be mostly limited to the sea shore where the WP is now scarce or absent, which could suggest competitive exclusion. Once clearly occurring in a sympatric context, the allochronic differentiation tends to develop nowadays in parapatry.