Stillwell RC, Fox CW. Environmental effects on sexual size dimorphism of a seed-feeding beetle. Oecologia 153: 273-280

Department of Entomology, University of Kentucky, S225 Agricultural Science Center North, Lexington, KY 40546-0091, USA.
Oecologia (Impact Factor: 3.09). 09/2007; 153(2):273-80. DOI: 10.1007/s00442-007-0724-0
Source: PubMed


Sexual size dimorphism is widespread in animals but varies considerably among species and among populations within species. Much of this variation is assumed to be due to variance in selection on males versus females. However, environmental variables could affect the development of females and males differently, generating variation in dimorphism. Here we use a factorial experimental design to simultaneously examine the effects of rearing host and temperature on sexual dimorphism of the seed beetle, Callosobruchus maculatus. We found that the sexes differed in phenotypic plasticity of body size in response to rearing temperature but not rearing host, creating substantial temperature-induced variation in sexual dimorphism; females were larger than males at all temperatures, but the degree of this dimorphism was smallest at the lowest temperature. This change in dimorphism was due to a gender difference in the effect of temperature on growth rate and not due to sexual differences in plasticity of development time. Furthermore, the sex ratio (proportion males) decreased with decreasing temperature and became female-biased at the lowest temperature. This suggests that the temperature-induced change in dimorphism is potentially due to a change in non-random larval mortality of males versus females. This most important implication of this study is that rearing temperature can generate considerable intraspecific variation in the degree of sexual size dimorphism, though most studies assume that dimorphism varies little within species. Future studies should focus on whether sexual differences in phenotypic plasticity of body size are a consequence of adaptive canalization of one sex against environmental variation in temperature or whether they simply reflect a consequence of non-adaptive developmental differences between males and females.

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    • "The geographic adaptations of animals, which include variations in body size, are generally genetically based (Armbruster, Bradshaw, Ruegg, & Holzapfel, 2001; Karl, Janowitz, & Fisher, 2008). Studies show that a thermocline (or other factors which vary with latitude or altitude) can result in both intra-specific and inter-specific size dimorphism (Blanckenhorn, Stillwell, Young, Fox, & Ashton, 2006; Stillwell & Fox, 2007; Teder & Tammaru, 2005). The body size of animals may also be correlated with population density (Robinson & Redford, 1986). "
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    ABSTRACT: As a general rule, spiders exhibit sexual dimorphism and their populations may differ in size according to season duration and resource availability. However, few studies have focused on dimorphism in tarantulas. Mexican redrump tarantulas, Brachypelma vagans, listed in CITES, have an exceptionally wide distribution. Surprisingly, there are no studies on the possible relationship between the abundance of tarantulas per population and the geographical areas where they are present, or on how the distribution pattern of this spider may affect individual morphological characteristics. Furthermore, there are no studies on sexual dimorphism within the genus Brachypelma. The aim of the study is to determine the existence of sexual and geographical dimorphism in populations of B. vagans. It was observed that the abundance of spiders per population may vary according to the geographical areas where they were recorded. In six localities in southern Mexico, we recorded morphological data on adult tarantulas. Sexual dimorphism was clearly observed at the site that presented numerous spiders characterized by much smaller females. Since the results of this study demonstrate differences in tarantula number of individuals per locality in southern Mexico, they make an important contribution to the conservation of this species.
    Revista Mexicana de Biodiversidad 09/2015; 86:737–743. DOI:10.1016/j.rmb.2015.07.003
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    • "Females may have displayed steeper size clines than males because their fi tness may be more sensitive to changes in season length, climatic variables, and the availability of food (Laiolo et al. 2013). Th is suggests diff erences in dispersal potential among species or populations may contribute to diff erences in geographic variation in sexual size dimorphism for a variety of taxa (but also see Stillwell and Fox 2007, 2009). As there is considerable evidence that long winged species such as M. sanguinipes are frequently dispersed to higher elevations along the Front Range of Colorado and that short winged species such as A. clavatus and M. boulderensis are not (Alexander 1951, 1964), it is important to note that some of the long winged individuals that were fi eld collected at higher sites may have originated from lower elevations. "
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    ABSTRACT: Body size is a life history trait that determines the reproductive success of a variety of organisms. Changes in body size may have a genetic component when persistent conditions such as season length and climate select for individuals of an optimal body size and an environmental component when it is influenced on an ecological scale by factors such as weather, food availability, or maternal effects. Along elevational gradients that experience seasonality, insects commonly become smaller with increases in elevation. In this study we test the hypothesis that dispersal potential, an indicator of gene flow, impacts the type of size clines exhibited by insects along elevational gradients and that these differences in local adaptation should lead to predictable changes in their reproductive potential and output. Using two short winged grasshopper species, Aeropedellus clavatus and Melanoplus boulderensis, and two long winged species, Camnula pellucida and Melanoplus sanguinipes, we showed that species with low dispersal potential are associated with significant declines in body size with increases in elevation while species with high dispersal potential displayed no size clines. Consistent with short winged species being more locally adapted, we show that reproductive potential, as measured by the proportion of ovarioles that become functional, do not differ among populations of short winged species, but decline with elevation in the long winged species. While our study failed to show that dispersal potential impacts reproductive output in a consistent and predictable manner (as measured by clutch and egg sizes), we address the possibility that clutch size may not reflect changes in total reproductive output and that changes in egg size may be a plastic trait. We concluded that studies exploring the evolution of body size, the reproductive capacity and species level responses to environmental change should note the importance of dispersal potential in influencing these patterns.
    Oikos 10/2014; 124(5). DOI:10.1111/oik.01615 · 3.44 Impact Factor
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    • "For example, female insects frequently exhibit greater phenotypic plasticity in body mass than males, creating variation in sexual size dimorphism within species [4]. Most of this sex difference in plasticity in size is in response to variation in diet quality and quantity, although some studies have shown that developmental temperature can also create sex-specific plasticity in size [22], [25], [26]. Because diet quality/quantity is known to be important in controlling insect growth and development and because it generates substantial sex-specific plasticity in body size, it is possible that diet quality/quantity will affect the ontogeny of sexual size dimorphism. "
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    ABSTRACT: Sexual dimorphism in body size (sexual size dimorphism) is common in many species. The sources of selection that generate the independent evolution of adult male and female size have been investigated extensively by evolutionary biologists, but how and when females and males grow apart during ontogeny is poorly understood. Here we use the hawkmoth, Manduca sexta, to examine when sexual size dimorphism arises by measuring body mass every day during development. We further investigated whether environmental variables influence the ontogeny of sexual size dimorphism by raising moths on three different diet qualities (poor, medium and high). We found that size dimorphism arose during early larval development on the highest quality food treatment but it arose late in larval development when raised on the medium quality food. This female-biased dimorphism (females larger) increased substantially from the pupal-to-adult stage in both treatments, a pattern that appears to be common in Lepidopterans. Although dimorphism appeared in a few stages when individuals were raised on the poorest quality diet, it did not persist such that male and female adults were the same size. This demonstrates that the environmental conditions that insects are raised in can affect the growth trajectories of males and females differently and thus when dimorphism arises or disappears during development. We conclude that the development of sexual size dimorphism in M. sexta occurs during larval development and continues to accumulate during the pupal/adult stages, and that environmental variables such as diet quality can influence patterns of dimorphism in adults.
    PLoS ONE 09/2014; 9(9):e106548. DOI:10.1371/journal.pone.0106548 · 3.23 Impact Factor
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