Explore the vast range of titles available.

Hybridization is increasingly being recognized as a widespread process, even between ecologically and behaviorally divergent animal species. Determining phylogenetic relationships in the presence of hybridization remains a major challenge for evolutionary biologists, but advances in sequencing technology and phylogenetic techniques are beginning to address these challenges. Here we reconstruct evolutionary relationships among swordtails and platyfishes (Xiphophorus: Poeciliidae), a group of species characterized by remarkable morphological diversity and behavioral barriers to interspecific mating. Past attempts to reconstruct phylogenetic relationships within Xiphophorus have produced conflicting results. Because many of the 26 species in the genus are interfertile, these conflicts are likely due to hybridization. Using genomic data, we resolve a high-confidence species tree of Xiphophorus that accounts for both incomplete lineage sorting and hybridization. Our results allow us to reexamine a long-standing controversy about the evolution of the sexually selected sword in Xiphophorus, and demonstrate that hybridization has been strikingly widespread in the evolutionary history of this genus.

Evolutionary drivers of the gain and loss of ornamentation are often unclear even for classic ornamentation such as swallows’ tails, because macroevolutionary analysis, which is needed to clarify the factors responsible for the transition, is rarely conducted. Some behavioural experiments support the hypothesis that sexual selection is responsible for the evolution of “forked” tails, while others support the hypothesis that foraging on large prey favours the evolution of forked tails. However, empirical tests of these hypotheses used already-ornamented species and macroevolutionary studies of forked/forkless tails, which is critical for inferring the evolutionary forces driving the transition between the presence and absence of ornamentation, are still lacking. Here, using a clade of swallows and martins (Aves: Hirundininae), we examined the evolutionary transition between forkless and forked tails in relation to measures of foraging mode and sexual selection. We found replicated evolution of forkless tails from forked tails, all in clades with sexually monomorphic plumage. Furthermore, we detected correlated evolution of tail shape (i.e., forkless/forked) and extrapair mating opportunity, measured as incubation type which is tightly linked to extrapair paternity both within and among species. A transition from forked to forkless tails was less likely to occur than the reverse transition when extrapair mating opportunities were readily available, but not when extrapair mating opportunities were limited. In contrast, the tail shape was more likely to evolve independently with prey size (i.e., small/large) and social foraging behaviour (i.e., social/solitary foraging). These findings indicate that the intensity of sexual selection, rather than foraging mode, explains the evolutionary transition between the presence and absence of tail ornamentation, questioning the widespread perspective that capturing large prey is an evolutionary force driving and maintaining forked tails.

Background The maintenance of considerable genetic variation in sexually selected traits (SSTs) is puzzling given directional selection expected to act on these traits. A possible explanation is the existence of a genotype-by-environment (GxE) interaction for fitness, by which elaborate SSTs are favored in some environments but selected against in others. In the current study, we look for such interactions for fitness-related traits in the bulb mite, a male-dimorphic species with discontinuous expression of a heritable SST in the form of enlarged legs that are used as weapons. Results We show that evolution at 18 °C resulted in populations with a higher prevalence of this SST compared to evolution at 24 °C. We further demonstrate that temperature modified male reproductive success in a way that was consistent with these changes. There was a genotype-by-environment interaction for reproductive success – at 18 °C the relative reproductive success of armored males competing with unarmored ones was higher than at the moderate temperature of 24 °C. However, male morph did not have interactive effects with temperature with respect to other life history traits (development time and longevity). Conclusions A male genotype that is associated with the expression of a SST interacted with temperature in determining male reproductive success. This interaction caused an elaborate SST to evolve in different directions (more or less prevalent) depending on the thermal environment. The implication of this finding is that seasonal temperature fluctuations have the potential to maintain male polymorphism within populations. Furthermore, spatial heterogeneity in thermal conditions may cause differences among populations in SST selection. This could potentially cause selection against male immigrants from populations in different environments and thus strengthen barriers to gene flow.

Background The expression of sexually selected traits often varies with populations’ breeding cycles in many animals. The elucidation of mechanisms underlying the expression of such traits is a research topic in evolutionary biology; however, the genetic basis of the seasonal development of their expression remains unknown. Male Leptobrachium boringii develop keratinized nuptial spines on their upper jaw during the breeding season that fall off when the breeding season ends. To illuminate the genetic basis for the expression of this trait and its seasonal development, we assessed the de novo transcriptome for L. boringii using brain, testis and upper jaw skin and compared gene expression profiles of these tissues between two critical periods of the spine growth cycle. Results We identified 94,900 unigenes in our transcriptome. Among them, 2,131 genes were differentially expressed between the breeding period when the spines developed and the post-breeding period when the spines were sloughed. An increased number of differentially expressed genes (DEGs) were identified in the upper jaw skin compared with the testis and brain. In the upper jaw skin, DEGs were mainly enriched in cytosolic part, peptidase inhibitor activity and peptidase regulator activity based on GO enrichment analysis and in glycolysis/gluconeogenesis, ribosome biogenesis in eukaryotes and retinol metabolism based on KEGG enrichment analysis. In the other two tissues, DEGs were primarily involved in the cell cycle, DNA replication and melatonin production. Specifically, insulin/insulin-like growth factor and sex steroid hormone-related DEGs were identified in the upper jaw skin. The expression variation of IGF2 and estrogen-related genes may be the main factors regulating the seasonal development of the spines. Conclusions Our study provides a list of potential genes involved in the regulation of seasonal development of nuptial spines in L. boringii . This is the first transcriptome survey of seasonally developed sexually selected traits for non-model amphibian species, and candidate genes provided here may provide valuable information for further studies of L. boringii.

1. Female preferences for particular male ornaments may shift between populations as a consequence of ecological differences that change the reliability and detectability of the ornament, but few studies have examined how ornaments function in different populations. 2. We examined the signalling function of male plumage ornaments in a warbler, the common yellowthroat (Geothlypis trichas), breeding in New York (NY) and Wisconsin (WI), USA. Males have two prominent ornaments: a black facial mask pigmented with melanin and a yellow bib pigmented by carotenoids. Previous studies in WI indicate that the size of the mask, and not the bib, is primarily related to female choice and male reproductive success. In NY, however, the pattern is reversed and attributes of the bib (size and colour), and not the mask, are the target of sexual selection. 3. We found that brightness of the yellow bib was the best signal of humoral immunity (immunoglobulin G) in NY and mask size was the best signal in WI, after controlling for breeding experience and capture date. Thus, similar aspects of male quality appeared to be signalled by different ornaments in different populations. 4. There was no difference between populations in the level of plasma carotenoids or the prevalence of malarial parasites, which may affect the costs and benefits of choosing males with particular ornaments in each location. 5. Even though females in different populations prefer different ornaments produced by different types of pigments, these ornaments appear to be signalling similar aspects of male quality. Our results caution against inferring the function of particular ornaments based simply on their type of pigment.

1. There is growing concern about the evolutionary consequences of human harvesting on phenotypic trait quality in wild populations. Undesirable consequences are especially likely with trophy hunting because of its strong bias for specific phenotypic trait values, such as large antlers in cervids and horns in bovids. Selective hunting can cause a decline in a trophy trait over time if it is heritable, thereby reducing the long-term sustainability of the activity itself. 2. How can we build a sustainable trophy hunting tradition without the negative trait-altering effects? We used an individual-based model to explore whether selective compensatory culling of 'low quality' individuals at an early life stage can facilitate sustainability, as suggested by information from managed game populations in eastern and central Europe. Our model was rooted in empirical data on red deer, where heritability of sexual ornaments has been confirmed and phenotypic quality can be assessed by antler size in individuals as young as 1 year. 3. Simulations showed that targeted culling of low-quality yearlings could counter the selective effects of trophy hunting on the distribution of the affected trait (e.g. antler or horn size) in prime-aged individuals. Assumptions of trait heritability and young-to-adult correlation were essential for compensation, but the model proved robust to various other assumptions and changes to input parameters. The simulation approach allowed us to verify responses as evolutionary changes in trait values rather than short-term consequences of altered age structure, density and viability selection. 4. We conclude that evolutionarily enlightened management may accommodate trophy hunting. This has far reaching implications as income from trophy hunting is often channelled into local conservation efforts and rural economies. As an essential follow-up, we recommend an analysis of the effects of trophy hunting in conjunction with compensatory culling on the phenotypic and underlying genetic variance of the trophy trait.

Organisms use environmental cues to time their life-cycles and among these cues, photoperiod is the main trigger of reproductive behaviours such as territory defence or song activity. Whether photoperiod is also important for another behaviour closely associated with reproduction, mate choice, is unknown. In many bird species, mate choice occurs at two different times during the annual cycle that strongly differ in daylength: in late winter when photoperiod is short and social mates are chosen, and again around egg-laying when photoperiod is longer and extra-pair mates are chosen. This duality makes the role that photoperiod plays on mate choice behaviours intriguing. We investigated the effect of photoperiod on mate choice using three experimental photoperiodic treatments (9 L:15 D, 14 L:10 D, 18 L:6 D), using blue tits (Cyanistes caeruleus) as a biological model. We show that female choice was stronger under long photoperiods. In addition, female blue tits spent significantly more time near males with long tarsi and long wings. This latter preference was only expressed under long photoperiods, suggesting that some indices of male quality only become significant to females when they are strongly photostimulated, and therefore that females could select their social and extra-pair mates based on different phenotypic traits. These results shed light on the roles that photoperiod may play in stimulating pair-bonding and in refining female selectivity for male traits.

Male insects with large weapons such as horns and elongate mandibles would be expected to invest more on such structures than other parts of the body for advantages in male to male competition for mating. In male genitalia, however, intermediate size provides a better fit for more females than small or large sizes, and such a male would leave more offspring regardless of their body size. These predictions were tested using a static allometry analysis between body size and other trait sizes. Acanthacorydalisasiatica is a large dobsonfly (Megalotera) and males have conspicuously large mandibles used as weapons. We examined the hypothesis that the male mandibles of this sexually dimorphic species are sexually selected to enlarge, whereas the male genitalia are stable to be intermediate regardless of a great variation in body size. The results, as predicted, showed positive allometry between male body size and mandible length but negative allometry between male body size and ectoproct length (a male grasping structure). Sperm are transferred through a small spermatophore attached externally to the female genital opening, so it may be evolutionarily unnecessary to develop an enlarged male genital size. In contrast, there may be a trade-off between male mandible size and wing length, because of negative allometry between body size and wing length in males but isometry between them in females.

Alternative reproductive tactics (ARTs) evolve to maximise fitness by favouring alternative phenotypes when high variance in relative fitness occurs amongst individuals. In the damselfly Hetaerina vulnerata males occur as either territorial or nonterritorial, depending on whether males acquire and defend an area to which females are attracted for copulation. Territorial males are usually larger, more pigmented and more successful in obtaining copulations than nonterritorial males. Several studies further suggest that territorial males are in overall better condition than nonterritorial ones. Other studies have investigated whether wing pigmentation, a sexual trait in damselflies, scales hyperallometrically with body size, and asked whether this pattern is related to fitness—nonetheless, a clear answer to this question remains elusive. Here we investigate whether i) territorial and nonterritorial males differed in body size and wing pigmentation; ii) body size, wing pigmentation and/or male status (male ART) predicted male mating success; and iii) the allometry of wing pigmentation in territorial and nonterritorial males, and amongst mated and unmated males. We first found that territorial and nonterritorial males did not differ in body size. Second, contrary to what occurs in other damselflies, territorial and nonterritorial males exhibited similar amounts of wing pigmentation. Third, only territory tenure, but not body size or wing pigmentation, predicted male mating success. Finally, with the exception of the relationship exhibited by mated males, which exhibited isometry, wing pigmentation was hyperallometric in all groups of males tested. The latter result suggests that hyperallometry of the sexual trait in this damselfly may not be selectively advantageous.

Here, we tested for an ecologically valid cost to secondary sexual trait expression in the male great tit (Parus major). We compared the breast stripe area of a sample of males who survived extremely low night time temperatures with a sample who did not survive. Breast stripe area was significantly smaller in surviving males, suggesting a real cost of signalling in terms of survival. The relationship between breast stripe area and survival was moderated by the effects of body condition: Males with larger breast stripes were in poorer condition and hence suffered increased mortality. Finally, we tested for relationships between breast stripe area and body condition, and tarsus asymmetry and immunological parameters (Brucella abortus antibody count, heterophil to lymphocyte ratio, eosinophil count, monocyte count) in surviving males. Only eosinophil count was related to breast stripe area. Our results suggest a survival cost to investment in sexual signals, such that males who invest somatic resources in social signalling risk increased mortality under extreme environmental conditions.