A Comparative Analysis of Allometry for Sexual Size Dimorphism: Assessing Rensch's Rule

Abouheif, Ehab; Fairbairn, Daphne J.

doi:10.1086/286004

Cited by 383 publications

(523 citation statements)

References 93 publications

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“…This leads us to the simple explanation that this strongly significant relationship is an outcome of similar T-S responses between males and females, which causes a greater absolute degree of size convergence and divergence as relative response increases; an outcome expected simply from mathematics, but one with possible ecological implications. Taxonomic order has no significant effect on convergence or divergence (F 16 figure 4). Hence there is strong divergence in the absolute size of the sexes with warming in Orthoptera, but convergence in the Cyclopoida and Diptera.…”

Section: Resultsmentioning

confidence: 99%

“…A variety of rules and theories have been formulated to explain variation in SSD, both between and within species [14][15][16]. Rensch's rule (RR) states that male body size varies more than female body size, irrespective of which sex is larger.…”

Section: Introductionmentioning

confidence: 99%

“…RR was originally formulated to describe the pattern seen across species within a related clade, but has since been tested within species to see if similar drivers exist at the intra-specific level [13,17]. Within a species, it predicts an increase in SSD with increasing body size in species where males are the larger sex, and a decrease in SSD with body size in species where females are larger [14,16]. One prominent general hypothesis (i.e.…”

Section: Introductionmentioning

confidence: 99%

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Equal temperature–size responses of the sexes are widespread within arthropod species

2015

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Sexual size dimorphism (SSD) is often affected by environmental conditions, but the effect of temperature on SSD in ectotherms still requires rigorous investigation. We compared the plastic responses of size-at-maturity to temperature between males and females within 85 diverse arthropod species, in which individuals of both sexes were reared through ontogeny under identical conditions with excess food. We find that the sexes show similar relative (proportional) temperature-body size (T-S) responses on average. The high degree of similarity occurs despite an analysis that includes a wide range of animal body sizes, variation in degree of SSD and differences in the sign of the T-S response. We find no support for Rensch's rule, which predicts greater variation in male size, or indeed the reverse, greater female size variation. SSD shows no systematic temperature dependence in any of the 17 arthropod orders examined, five of which (Diptera, Orthoptera, Lepidoptera, Coleoptera and Calanoida) include more than six thermal responses. We suggest that the same proportional T-S response may generally have equivalent fitness costs and benefits in both sexes. This contrasts with effects of juvenile density, and food quantity/quality, which commonly result in greater size plasticity in females, suggesting these variables have different adaptive effects on SSD.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Equal temperature–size responses of the sexes are widespread within arthropod species

2015

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“…The fact that relationships are commonly not distinguishable from being isometric in many copepod clades suggests that selection on each of the sexes may have been near equally important. Most previous empirical assessments of allometry have focused on either vertebrates or invertebrates with male-biased SSD ( [3,6,7], cf. 8]) and in many of these studies the allometric slope within clades often decreases as the magnitude of SSD increases (see fig.…”

Section: Discussion (A) Allometry Of Sexual Size Dimorphismmentioning

confidence: 99%

Macroevolutionary patterns of sexual size dimorphism in copepods

Hirst

Kiørboe

2014

Proc. R. Soc. B.

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Major theories compete to explain the macroevolutionary trends observed in sexual size dimorphism (SSD) in animals. Quantitative genetic theory suggests that the sex under historically stronger directional selection will exhibit greater interspecific variance in size, with covariation between allometric slopes (male to female size) and the strength of SSD across clades. Rensch's rule (RR) also suggests a correlation, but one in which males are always the more size variant sex. Examining free-living pelagic and parasitic Copepoda, we test these competing predictions. Females are commonly the larger sex in copepod species. Comparing clades that vary by four orders of magnitude in their degree of dimorphism, we show that isometry is widespread. As such we find no support for either RR or for covariation between allometry and SSD. Our results suggest that selection on both sexes has been equally important. We next test the prediction that variation in the degree of SSD is related to the adult sex ratio. As males become relatively less abundant, it has been hypothesized that this will lead to a reduction in both inter-male competition and male size. However, the lack of such a correlation across diverse free-living pelagic families of copepods provides no support for this hypothesis. By comparison, in sea lice of the family Caligidae, there is some qualitative support of the hypothesis, males may suffer elevated mortality when they leave the host and rove for sedentary females, and their femalebiased SSD is greater than in many free-living families. However, other parasitic copepods which do not appear to have obvious differences in sex-based mate searching risks also show similar or even more extreme SSD, therefore suggesting other factors can drive the observed extremes.

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“…It is easy to imagine how sexual selection for larger size in males could lead to evolution of larger size in females as a correlated trait. This has likely played a major role in certain lineages of mammals, where there have been evolutionary trends for the body size to increase [Cope's rule (19)] and with increasing overall size for the ratio of male to female size also to increase [Rensch's rule (29,31)]. Eventually, species of very large size may go extinct, because their lower reproductive capacities and smaller populations increase their vulnerability to environmental change.…”

Section: Evolution Of Larger Body Sizementioning

confidence: 99%

Life-history evolution under a production constraint

Brown

Sibly

2006

Proc. Natl. Acad. Sci. U.S.A.

143

134

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The recently formulated metabolic theory of ecology has profound implications for the evolution of life histories. Metabolic rate constrains the scaling of production with body mass, so that larger organisms have lower rates of production on a mass-specific basis than smaller ones. Here, we explore the implications of this constraint for life-history evolution. We show that for a range of very simple life histories, Darwinian fitness is equal to birth rate minus death rate. So, natural selection maximizes birth and production rates and minimizes death rates. This implies that decreased body size will generally be favored because it increases production, so long as mortality is unaffected. Alternatively, increased body size will be favored only if it decreases mortality or enhances reproductive success sufficiently to override the preexisting production constraint. Adaptations that may favor evolution of larger size include niche shifts that decrease mortality by escaping predation or that increase fecundity by exploiting new abundant food sources. These principles can be generalized to better understand the intimate relationship between the genetic currency of evolution and the metabolic currency of ecology.allometry ͉ life-history theory ͉ metabolic ecology T he recently formulated metabolic theory of ecology (1) predicts that many attributes of individuals, populations, communities, and ecosystems should be relatively straightforward consequences of the metabolic processes of the relevant organisms. Specifically, many rate processes should scale with body size and temperature in the same way as mass-specific metabolic rate:where R is the rate of some biological process, R 0 is a normalization constant, the M Ϫ1/4 term gives the power-function dependence on body mass M, and the e ϪE/kT term or Boltzmann factor gives the exponential temperature dependence in terms of an ''activation energy'', E, Boltzmann's constant, k, and temperature, T, in Kelvin. This very general relationship holds both within and between species. It can be applied to the rate of production of biomass per unit mass, which is predicted to scale as M Ϫ1/4 (e.g., refs. 2-4). If we ignore temperature or assume for the moment that it does not vary, the Boltzmann factor is a constant. Then, taking logarithms of Eq. 1 we have log (mass-specific production rate) log (body mass). [2]This prediction appears to be generally supported, although for some traits, the empirically measured scaling exponents appear to deviate from the predicted Ϫ1͞4, sometimes being closer to Ϫ1͞3 (e.g., ref. 5). For our argument here, however, the exact value of the exponent is not an issue; what is important is that it is negative. The consequence of the negative exponent is that in a log-log plot, mass-specific production rate is a declining straight-line function of body mass, as shown schematically by the solid black line in Fig. 2 A. We take this to be a fundamental causal constraint limiting life-history options as suggested by metabolic theory. The result is that sm...

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A Comparative Analysis of Allometry for Sexual Size Dimorphism: Assessing Rensch's Rule

Cited by 383 publications

References 93 publications

Equal temperature–size responses of the sexes are widespread within arthropod species

Equal temperature–size responses of the sexes are widespread within arthropod species

Macroevolutionary patterns of sexual size dimorphism in copepods

Life-history evolution under a production constraint

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