Natural selection on body size is mediated by multiple interacting factors: A comparison of beetle populations varying naturally and experimentally in body size

Ecology and Evolution (Impact Factor: 2.32). 09/2011; 1(1):1-14. DOI: 10.1002/ece3.1
Source: PubMed


Body size varies considerably among species and among populations within species, exhibiting many repeatable patterns. However, which sources of selection generate geographic patterns, and which components of fitness mediate evolution of body size, are not well understood. For many animals, resource quality and intraspecific competition may mediate selection on body size producing large-scale geographic patterns. In two sequential experiments, we examine how variation in larval competition and resource quality (seed size) affects the fitness consequences of variation in body size in a scramble-competing seed-feeding beetle, Stator limbatus. Specifically, we compared fitness components among three natural populations of S. limbatus that vary in body size, and then among three lineages of beetles derived from a single base population artificially selected to vary in size, all reared on three sizes of seeds at variable larval density. The effects of larval competition and seed size on larval survival and development time were similar for larger versus smaller beetles. However, larger-bodied beetles suffered a greater reduction in adult body mass with decreasing seed size and increasing larval density; the relative advantage of being large decreased with decreasing seed size and increasing larval density. There were highly significant interactions between the effects of seed size and larval density on body size, and a significant three-way interaction (population-by-density-by-seed size), indicating that environmental effects on the fitness consequences of being large are nonadditive. Our study demonstrates how multiple ecological variables (resource availability and resource competition) interact to affect organismal fitness components, and that such interactions can mediate natural selection on body size. Studying individual factors influencing selection on body size may lead to misleading results given the potential for nonlinear interactions among selective agents.

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    • "), high temporal variation in resource availability (McLain, 1993; Badyaev & Ghalambor , 1998; Lehman et al., 2005) and/or high levels of resource competition (Amarillo-Su arez et al., 2011). One of the clearest examples of this is with the marine iguanas of the Galapagos (Wikelski & Trillmich, 1997; Wikelski et al., 1997; Wikelski, 2005). "
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    ABSTRACT: Understanding the evolution of body size and sexual size dimorphism has been a longstanding goal in evolutionary biology. Previous work has shown that environmental stress can constrain male-biased sexual size dimorphism at the population level, but we know little about how this might translate to geographical patterns of body size and sexual size dimorphism at the species level. Environmental constraints due to a highly seasonal, resource-poor and/or variable environment have often been cited to explain the unusual lack of sexual size dimorphism among Madagascar's diverse and numerous primate taxa; however, empirical tests of this hypothesis are lacking. Using a phylogenetic approach and a geographical information system platform, we explored the role of seasonality, interannual variability and annual measures of temperature and rainfall, and net primary productivity on patterns of body size and sexual size dimorphism across 130 species of primates. Phylogenetically controlled comparisons showed no support for a role of environmental constraints in moderating sexual size dimorphism at the interspecific level, despite significant associations of environmental variables with body mass. Results suggest that the focus of discussions that have dominated in the last two decades regarding the role of environmental constraints in driving patterns of monomorphism of Madagascar's lemurs should be reconsidered; however, the conundrum remains.
    Journal of Evolutionary Biology 09/2013; 26(11). DOI:10.1111/jeb.12239 · 3.23 Impact Factor
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    • "Many laboratory rearing experiments are performed under what researchers hope are optimal conditions, but discovery of trade-offs associated with increased growth rates are most likely when conditions are suboptimal (Fisher et al. 2007; Dmitriew 2011). Beetles selected for large size suffered a greater reduction in body mass when reared under stressful conditions such as being fed on small seeds or reared at high larval density (Amarillo-Suarez et al. 2011). Yellow dung flies selected for large size grew fast on optimal diets, but showed more strongly reduced growth and greater mortality than control lines or lines selected for small sizes when reared under food-restricted conditions, supporting the idea that stressful conditions reveal costs of large size/high growth rates (Teuschl et al. 2006; Blanckenhorn et al. 2011). "
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    ABSTRACT: Recent studies suggest that higher growth rates may be associated with reduced capacities for stress tolerance and increased accumulated damage due to reactive oxygen species. We tested the response of Manduca sexta (Sphingidae) lines selected for large or small body size and short development time to hypoxia (10 kPa) and hyperoxia (25, 33, and 40 kPa); both hypoxia and hyperoxia reduce reproduction and oxygen levels over 33 kPa have been shown to increase oxidative damage in insects. Under normoxic (21 kPa) conditions, individuals from the large-selected (big-fast) line were larger and had faster growth rates, slightly longer developmental times, and reduced survival rates compared to individuals from a line selected for small size (small-fast) or an unselected control line. Individuals from the big-fast line exhibited greater negative responses to hyperoxia with greater reductions in juvenile and adult mass, growth rate, and survival than the other two lines. Hypoxia generally negatively affected survival and growth/size, but the lines responded similarly. These results are mostly consistent with the hypothesis that simultaneous acquisition of large body sizes and short development times leads to reduced capacities for coping with stressful conditions including oxidative damage. This result is of particular importance in that natural selection tends to decrease development time and increase body size.
    Ecology and Evolution 05/2013; 3(5):1305-16. DOI:10.1002/ece3.551 · 2.32 Impact Factor
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    • "Demographic consequences of endogenous traits such as body size (e.g., Amarillo–Suárez et al. 2011, and references therein) are known. Under controlled conditions, for instance, the expected initial advantage of large-sized invertebrates is affected by resource quality and increasing competition already at early life stages (Amarillo–Suárez et al. 2011). In terrestrial biota, controversy exists over whether demographic responses reported from experimental conditions might reflect ecosystem functioning (Waide et al. 1999; Hooper et al. 2005; Crutsinger et al. 2006, etc.) and environmental conditions (Crutsinger et al. 2006; Mulder and Elser 2009). "
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    ABSTRACT: Nematodes are presumably the most numerous Metazoans in terrestrial habitats. They are represented at all trophic levels and are known to respond to nutrient limitation, prey availability, and microbial resources. Predatory nematodes reside at the highest trophic level, and as such their feeding habits could have a major impact on soil food web functioning. Here, we investigate the effects of gender and developmental stage on the nematode body sizes in coarse and loamy soils. Besides Neodiplogasteridae, our predators are much larger than other soil-dwelling nematodes from their early developmental stage onwards. From juvenile to adult, the predatory Aporcelaimellus (Kruskal-Wallis P < 0.001), Dorylaimoides, and Tripyla (both P < 0.01) show great length increases during their developmental growth, in contrast to their possible prey (almost all P < 0.001). Less than 4% of the prey exceeds the length of the predatory adults, but more than 30% of the prey exceeds the length of the predatory juveniles. Potential body size ratios and some physical problems experienced by small fluid feeders attacking large prey are discussed in an attempt to summarize different prey-searching mechanisms and aggregative predatory responses in the soil system.
    Ecology and Evolution 11/2011; 1(3):386-391. DOI:10.1002/ece3.36 · 2.32 Impact Factor
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