Mathieu J. Oudin

Bio: Mathieu J. Oudin is an academic researcher from University of Ottawa. The author has contributed to research in topics: Sexual dimorphism & Sexual selection. The author has an hindex of 2, co-authored 2 publications receiving 14 citations.

Experimental evidence of condition‐dependent sexual dimorphism in the weakly dimorphic antler fly Protopiophila litigata (Diptera: Piophilidae)

Abstract: Sexually dimorphic traits have a history of directional selection for exaggeration in at least one sex. Theory suggests that traits targeted by persistent selection should evolve heightened condition dependence whereby their expression reflects the availability and processing efficiency of metabolic resources. This joint dependence of sexual dimorphism and condition dependence on directional selection should result in a positive correlation between the extent of sexual dimorphism and the strength of condition dependence. However, because direct phenotypic evidence is predominately from species with highly exaggerated male traits, it remains unclear whether condition-dependent sexual dimorphism is characteristic of species with more typical levels of dimorphism. We manipulated condition via larval diet and quantified sex-specific responses in adult body size and shape in a moderately dimorphic dipteran species, the antler fly Protopiophila litigata. While dimorphism did not increase with diet quality within any trait, among traits the extent of dimorphism was positively associated with the strength of condition dependence in males but not females, as previously reported for highly dimorphic species. This finding suggests that a shared developmental basis to condition dependence and sexual dimorphism can arise via sexual selection on males even in lineages lacking highly exaggerated male traits. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 116, 211–220.

Development time mediates the effect of larval diet on ageing and mating success of male antler flies in the wild.

Abstract: High-quality developmental environments often improve individual performance into adulthood, but allocating toward early life traits, such as growth, development rate and reproduction, may lead to trade-offs with late-life performance. It is, therefore, uncertain how a rich developmental environment will affect the ageing process (senescence), particularly in wild insects. To investigate the effects of early life environmental quality on insect life-history traits, including senescence, we reared larval antler flies (Protopiophila litigata) on four diets of varying nutrient concentration, then recorded survival and mating success of adult males released in the wild. Declining diet quality was associated with slower development, but had no effect on other life-history traits once development time was accounted for. Fast-developing males were larger and lived longer, but experienced more rapid senescence in survival and lower average mating rate compared to slow developers. Ultimately, larval diet, development time and body size did not predict lifetime mating success. Thus, a rich environment led to a mixture of apparent benefits and costs, mediated by development time. Our results indicate that 'silver spoon' effects can be complex and that development time mediates the response of adult life-history traits to early life environmental quality.

The evolution of male-biased sexual size dimorphism is associated with increased body size plasticity in males

Abstract: 1. Sexual size dimorphism (SSD) can vary drastically across environments, demonstrating pronounced sex-specific plasticity. In insects, females are usually the larger and more plastic sex. However, the shortage of taxa with male-biased SSD hampers the assessment of whether the greater plasticity in females is driven by selection on size or represents an effect of the female reproductive role. Here, we specifically address the role of sex-specific plasticity of body size in the evolution of SSD reversals to disentangle sex and size effects. 2. We first investigate sex-specific body size plasticity in Sepsis punctum and Sepsis neocynipsea as two independent cases of intraspecific SSD reversals in sepsid flies. In both species, directional variation in SSD between populations is driven by stronger sexual selection on male size. Using controlled laboratory breeding, we find evidence for sex-specific plasticity and increased condition dependence of male size in populations with male-biased SSD, but not of female size in populations with female-biased SSD. 3. To extend the comparative scope, we next estimate sex-specific body size plasticity in eight additional fly species that differ in the direction of SSD under laboratory conditions. In all species with male-biased SSD we find males to be the more plastic sex, while this was only rarely the case in species with female-biased SSD, thus suggesting a more general trend in Diptera. 4. To examine the generality of this pattern in holometabolous insects, we combine our data with data from the literature in a meta-analysis. Again, male body size tends to be more plastic than female size when males are the larger sex, though female size is now also generally more plastic when females are larger. 5. Our findings indicate that primarily selection on size, rather than the reproductive role per se, drives the evolution of sex-specific body size plasticity. However, sepsid flies, and possibly Diptera in general, show a clear sexual asymmetry with greater male than female plasticity related to SSD, likely driven by strong sexual selection on males. Although further research controlling for phylogenetic and ecological confounding effects is needed, our findings are congruent with theory in suggesting that condition dependence plays a pivotal role in the evolution of sexual size dimorphism.

Sexual dimorphism and heightened conditional expression in a sexually selected weapon in the Asian rhinoceros beetle.

Abstract: Among the most dramatic examples of sexual selection are the weapons used in battles between rival males over access to females. As with ornaments of female choice, the most "exaggerated" sexually selected weapons vary from male to male more widely than other body parts (hypervariability), and their growth tends to be more sensitive to nutritional state or physiological condition compared with growth of other body parts ("heightened" conditional expression). Here, we use RNAseq analysis to build on recent work exploring these mechanisms in the exaggerated weapons of beetles, by examining patterns of differential gene expression in exaggerated (head and thorax horns) and non-exaggerated (wings, genitalia) traits in the Asian rhinoceros beetle, Trypoxylus dichotomus. Our results suggest that sexually dimorphic expression of weaponry involves large-scale changes in gene expression, relative to other traits, while nutrition-driven changes in gene expression in these same weapons are less pronounced. However, although fewer genes overall were differentially expressed in high- vs. low-nutrition individuals, the number of differentially expressed genes varied predictably according to a trait's degree of condition dependence (head horn > thorax horn > wings > genitalia). Finally, we observed a high degree of similarity in direction of effects (vectors) for subsets of differentially expressed genes across both sexually dimorphic and nutritionally responsive growth. Our results are consistent with a common set of mechanisms governing sexual size dimorphism and condition dependence.

The tale of the shrinking weapon: seasonal changes in nutrition affect weapon size and sexual dimorphism, but not contemporary evolution.

Abstract: Sexually-selected traits are often highly variable in size within populations due to their close link with the physical condition of individuals. Nutrition has a large impact on physical condition, and thus any seasonal changes in nutritional quality are predicted to alter the average size of sexually-selected traits as well as the degree of sexual dimorphism in populations. However, while traits affected by mate choice are well-studied, we have a surprising lack of knowledge of how natural variation in nutrition affects the expression of sexually-selected weapons and sexual dimorphism. Further, few studies explicitly test for differences in the heritability and mean-scaled evolvability of sexually-selected traits across conditions. Using the insect, Narnia femorata (Hemiptera: Coreidae), an insect where males use their hind legs as weapons and the femurs are enlarged, we studied the extent to which weapon expression, sexual dimorphism, and evolvability change across the actual range of nutrition available in the wild. We found that insects raised on a poor diet (cactus without fruit) are nearly monomorphic, while those raised on a high quality diet (cactus with ripe fruit) are distinctly sexually dimorphic via the expression of large hind leg weapons in males. Contrary to our expectations, we found little evidence of a potential for evolutionary change for any trait measured. Thus, although we show weapons are highly condition dependent, and changes in weapon expression and dimorphism could alter evolutionary dynamics, our populations are unlikely to experience further evolutionary changes under current conditions. This article is protected by copyright. All rights reserved.

A Comparative Study of the Role of Sex-Specific Condition Dependence in the Evolution of Sexually Dimorphic Traits.

Abstract: Sexual selection can displace traits acting as ornaments or armaments from their viability optimum in one sex, ultimately giving rise to sexual dimorphism. The degree of dimorphism should n...

Resource quality affects weapon and testis size and the ability of these traits to respond to selection in the leaf-footed cactus bug, Narnia femorata

Abstract: The size of weapons and testes can be central to male reproductive success. Yet, the expression of these traits is often extremely variable. Studies are needed that take a more complete organism perspective, investigating the sources of variation in both traits simultaneously and using developmental conditions that mimic those in nature. In this study, we investigated the components of variation in weapon and testis sizes using the leaf-footed cactus bug, Narnia femorata (Hemiptera: Coreidae) on three natural developmental diets. We show that the developmental diet has profound effects on both weapon and testis expression and scaling. Intriguingly, males in the medium-quality diet express large weapons but have relatively tiny testes, suggesting complex allocation decisions. We also find that heritability, evolvability, and additive genetic variation are highest in the high-quality diet for testis and body mass. This result suggests that these traits may have an enhanced ability to respond to selection during a small window of time each year when this diet is available. Taken together, these results illustrate that normal, seasonal fluctuations in the nutritional environment may play a large role in the expression of sexually selected traits and the ability of these traits to respond to selection.