Biology subjects

Felmy, A.

Publications and source records attributed to Felmy, A..

8 recordsLinked to original sources

bioRxiv2026

Polygyny carries costs in both sexes in Trinidadian guppies

According to sexual selection theory, males should benefit more from mating with multiple partners than females do, as male investment into offspring production is typically lower. For females, empirical evidence indeed often shows diminishing returns or even costs of mating multiply. For males, the assumption often seems to be "the more, the better" - i.e., a steady increase of male reproductive success with mate number - but experimental tests of it are rare. Here we used a laboratory experiment with Trinidadian guppies (Poecilia reticulata), known for being promiscuous, to assess how pairing males weekly with 4 vs. 7 females affects both sexes reproductive performance (n = 32 polygynous males and 170 monogamous females). Increased polygyny delayed females reproductive onset by 9% and tripled their risk of reproductive failure. High-polygyny males fathered offspring with 49% more females and had 73% higher daily reproductive output. Yet, they needed 19% longer to initiate pregnancy, and only accumulated more offspring than low-polygyny males after two months. This study suggests that male mating performance is not unlimited. Especially when high extrinsic mortality selects for fast reproduction, less polygyny might be advantageous, and the strength of sexual selection perhaps more similar between the sexes than often assumed.

evolutionary biology↗

bioRxiv2022

Why the architecture of environmental fluctuation matters for fitness

The physical environment provides the very stage upon which the eco-evolutionary play unfolds. How fluctuations in the environment affect demographic fitness is thus central to selection predictions, life history analyses, and viability of populations. Treatment of fluctuating environments typically leverages the mathematics of random variability. However, environmental fluctuations in nature are almost always combinations of random and non-random components. For example, some fluctuations contain feedbacks which generate autocorrelation (e.g. disturbances such as floods, fires, and hurricanes), while others are driven by geophysical forces that create fixed cyclicality (e.g. seasonal, tidal, and diel). Despite theoretical developments, the consideration of non-random characteristics of fluctuations is still rare in empirical work on natural populations, mostly due to convention and partially due to difficulties in measuring and analyzing timeseries of environmental fluctuations. We show why non-randomness matters for fitness. Using a simple demographic model, we systematically compare four major categories of fluctuating environments: stochastic, positively autoregressive, negatively autoregressive, and periodic with error ("Noisy Clock"). The architectures of fluctuations influence the fitness of structured populations even when the modelled environments only differ in the timing of fluctuations, and not in their overall frequency. Importantly, we highlight two quantitative mechanisms through which fitness depends on fluctuation architecture--the consecutiveness of deviations from the environmental mean, and Jensens Inequality acting on nonlinear biological parameters--both relevant features in virtually all populations inhabiting variable environments. Our goal is to argue that non-random structures of environmental variability should be more seriously considered in empirical work. Such an endeavor would tap into the rich diversity of variable environments in nature to expand our understanding of the commensurate diversity of population dynamics.

ecology↗

bioRxiv2022

Density dependent environments can select for extremes of body size

Body size variation is an enigma. We do not understand why species achieve the sizes they do, and this means we also do not understand the circumstances under which gigantism or dwarfism is selected. We develop size-structured integral projection models to explore evolution of body size and life history speed. We make few assumptions and keep models simple: all functions remain constant across models except for the one that describes development of body size with age. We set sexual maturity to occur when size attains 80% of the asymptotic size, which is typical of a large mammal, and allow negative density dependence to only affect either reproduction or juvenile survival. Fitness - the quantity that is maximized by adaptive evolution - is carrying capacity in our models, and we are consequently interested in how it changes with size at sexual maturity, and how this association varies with development rate. The simple models generate complex dynamics while providing insight into the circumstances when extremes of body size evolve. The direction of selection leading to either gigantism or dwarfism crucially depends on the proportion of the population that is sexually mature, which in turn depends on how the development function determines the survivorship schedule. The developmental trajectories consequently interact with size-specific survival or reproductive rates to determine the best life history and the optimal body size emerges from that interaction. These dynamics result in trade-offs between different components of the life history, with the form of the trade-off that emerges depending upon where in the life history density dependence operates most strongly. Empirical application of the approach we develop has potential to help explain the enigma of body size variation across the tree of life.

evolutionary biology↗

bioRxiv2021

Cryptic individual-level variation in propensity for selfing in a hermaphroditic snail

For mating-system evolution, individual-level variation is essential. In self-compatible hermaphrodites, individuals may vary in their lifetime propensity for selfing, which consists of individual and environmental components. According to the reproductive assurance hypothesis explaining partial selfing, a key environmental factor is mate availability, which fluctuates with population density. We quantified individual variation in selfing propensity in a hermaphroditic snail by manipulating mate availability, recording mating behaviour, estimating selfing rates from progeny arrays, and measuring female lifetime fitness. We found substantial among-individual variation in selfing propensity, including pure outcrossers, pure selfers, and two types of plastic individuals. This variation only manifested in the laboratory; for the highly dense field population, data suggest full outcrossing. Meanwhile, experimental levels of mate availability (low versus moderate) neither significantly affected selfing propensities nor selfing rates. Instead, selfing propensities had an individual, environment-independent component. Our results imply that selfing propensities are partially heritable and, when selected on, cause mean selfing rates to evolve. We propose that genetic variation in selfing propensities offers a reconciliation between the reproductive assurance hypothesis and its limited empirical support in animals: distributions of selfing propensities vary temporally and spatially, thus obscuring the relationship between population density and realised selfing rates.

evolutionary biology↗

bioRxiv2021

An ecological explanation for hyperallometric scaling of reproduction

In wild populations, large individuals have disproportionately higher reproductive output than smaller individuals. Some theoretical models explain this pattern - termed reproductive hyperallometry - by individuals allocating a greater fraction of available energy towards reproductive effort as they grow. Here, we propose an ecological explanation for this observation: differences between individuals in rates of resource assimilation, where greater assimilation causes both increased reproduction and body size, resulting in reproductive hyperallometry at the level of the population. We illustrate this effect by determining the relationship between size and reproduction in wild and lab-reared Trinidadian guppies. We show that (i) reproduction increased disproportionately with body size in the wild but not in the lab, where resource competition was eliminated and food availability restricted; (ii) in the wild, hyperallometry was greatest during the wet season, when resource competition is strongest; and (iii) detection of hyperallometric scaling of reproduction at the population level was inevitable if individual differences in assimilation were ignored. We propose that ecologically-driven variation in assimilation - caused by size-dependent resource competition, niche expansion, and chance - contributes substantially to hyperallometric scaling of reproduction in natural populations. We recommend that mechanistic models incorporate such ecologically-caused variation when seeking to explain reproductive hyperallometry.

ecology↗

bioRxiv2021

Life histories as mosaics: plastic and genetic components differ among traits that underpin life-history strategies

Life-history variation reflects phenotypic variation across suites of traits. Differences among life-history strategies result from genetic differentiation, phenotypic plasticity, and genotype-by-environment interactions. If the relative strength and direction of these components differed among traits underlying a strategy, life histories might not evolve as a cohesive unit. We tested this hypothesis on the high- and low-predation ecotypes of Trinidadian guppies, defined by distinct life-history strategies. Using common garden experiments, we assessed how strongly 36 traits were determined by ancestral habitat (i.e., ecotype) or food availability, a key environmental difference between ecotypes. Our dataset was large (1178 individuals) and included six putatively independent origins of the derived ecotype. Traits could be confidently assigned to four groups, defined by highly significant effects of only food (13 traits), only habitat (6), both (6), or neither (11), revealing substantial variation among traits in levels of genetic and environmental control. Ecotype-food (i.e., genotype-by-environment) interactions were negligible. The directions of plastic and genetic effects were usually aligned. This suggests that life histories are mosaics with unequal rates of phenotypic and evolutionary change. Broadly speaking of "life-history evolution" masks a complex interplay of genes and environment on the multiple traits that underpin life-history strategies.

evolutionary biology↗

bioRxiv2020

Ancestral ecological regime shapes reaction to food limitation in the Least Killifish, Heterandria formosa

In populations with contrasting densities of conspecifics, we often see genetically-based differences in life histories. The divergent life histories could be driven by several distinct agents of selection, including, amongst other factors, variation in per-capita food levels, the intensity of crowding-induced stress, rates of pathogen transmission, mate encounter rates, and the rates with which waste products accumulate. Understanding which selective agents act in a particular population is important as the type of agents can affect both population dynamics and evolutionary responses to density-dependent selection. Here we used a full-factorial laboratory experiment to examine whether two populations of a small live-bearing freshwater fish, characterised by high-density/low-predation or low-density/high-predation conditions, are adapted to different per-capita food levels. As expected, fish from the higher density regime handled food limitation better than those from the lower density regime. Although the lower food level resulted in slower growth, smaller body size, delayed maturation and reduced survival in both populations, especially survival to maturity showed a highly significant population x food-level interaction. At low food, 75% of fish from the low-density population died, compared to only 15% of fish from the high-density population. This difference was much smaller at high food (15% vs. 0% mortality), and was mediated, at least partly, through a larger size at birth of fish from the high-density regime. While we cannot preclude other agents of selection from operating differently in the study populations, we demonstrate that selection at higher density confers a greater ability to cope with low per-capita food availability.

evolutionary biology↗

bioRxiv2019

Fitness functions, genetic and non-genetic inheritance, and why ecological dynamics and evolution are inevitably linked

The Breeders and Price equations are static models of evolution. Recent work has demonstrated how components of these equations, such as selection differentials and heritabilities, can be calculated for each time-step from dynamic, evolutionarily-explicit, structured population models. These dynamic models consist of functions that describe how environmental factors impact associations of genotypes and phenotypic traits with survival, reproduction, development, and non-genetic inheritance. Because evolutionarily explicit versions of these structured models can include feedbacks and can capture all the routes via which environmental variation can impact evolution, they i) provide a more powerful predictive tool for modelling eco-evolution in natural settings than existing approaches, and ii) reveal how key evolutionary parameters incorporated into static models change with time as evolution, or environmental change, proceeds.

evolutionary biology↗