Matters of scale : positive allometry and the evolution of male dimorphisms

J.L.T. was funded by a Biotechnology and Biological Sciences Research Council research fellowship, J.S.K. by the Academy of Finland, and N.R.L. by a Natural Environment Research Council research fellowship.The developmental independence of alternative phenotypes is key to evolutionary theories of phenotypic plasticity and the origins of diversity. Male dimorphisms associated with alternative reproductive tactics are widely cited examples of such facultative expression of divergent fitness optima. Current models for the evolution of male dimorphisms invoke a size-dependent threshold at which the phenotype is reprogrammed. We use predictions derived from allometric modeling to test for the existence of reprogramming thresholds in two species of beetle, Onthophagus taurus and Onthophagus binodis, and the European earwig Forficula auricularia. We also compare the allometry of a number of morphological traits to determine whether minor males suppress their secondary sexual traits. The intercept of the horn allometry was suppressed, but there was no evidence of reprogramming of horn growth in either beetle species. There was reprogramming in the earwig. In the beetles, the horn length in all males can be explained largely in terms of exponential horn growth following an extraordinarily steep power function. The asymptote in O. taurus can be explained by exponential growth meeting the constraint of resource exhaustion. These findings question the currently held view that beetle horn dimorphisms showcase the importance of developmental independence in the evolution of diversity.Publisher PDFPeer reviewe

Ownership-dependent mating tactics of minor males of the beetle Librodor japonicus (Nitidulidae) with intra-sexual dimorphism of mandibles

Intra-sexual dimorphism is found in the weapons of many male beetles. Different behavioral tactics to access females between major and minor males, which adopt fighting and alternative tactics, respectively, are thought to maintain the male dimorphism. In these species major males have enlarged weapons that they use in fights with rival males. Minor males also have small weapons in some of these species, and it is unclear why these males possess weapons. We examined the hypothesis that minor males might adopt a fighting tactic when their status was relatively high in comparison with that of other males (e.g., ownership of a territory). We observed the behavioral tactics of major and minor males of the beetle Librodor japonicus, whose males have a dimorphism of their mandibles. Major males fought for resources, whereas minor males adopted two status-dependent tactics, fighting and sneaking, to access females, depending on their ownership of a sap site. We suggest that ownership status-dependent mating tactics in minor males may maintain the intra-sexual dimorphism in this beetle.</p

How to halt the global decline of lands

The assessment of land degradation and restoration by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services shows that land degradation across the globe is a wide and severe issue and is showing no signs of slowing down. This trend must be halted and reversed

Good Genes and Sexual Selection in Dung Beetles (Onthophagus taurus): Genetic Variance in Egg-to-Adult and Adult Viability

Whether species exhibit significant heritable variation in fitness is central for sexual selection. According to good genes models there must be genetic variation in males leading to variation in offspring fitness if females are to obtain genetic benefits from exercising mate preferences, or by mating multiply. However, sexual selection based on genetic benefits is controversial, and there is limited unambiguous support for the notion that choosy or polyandrous females can increase the chances of producing offspring with high viability. Here we examine the levels of additive genetic variance in two fitness components in the dung beetle Onthophagus taurus. We found significant sire effects on egg-to-adult viability and on son, but not daughter, survival to sexual maturity, as well as moderate coefficients of additive variance in these traits. Moreover, we do not find evidence for sexual antagonism influencing genetic variation for fitness. Our results are consistent with good genes sexual selection, and suggest that both pre- and postcopulatory mate choice, and male competition could provide indirect benefits to females

Sexual Display and Mate Choice in an Energetically Costly Environment

Sexual displays and mate choice often take place under the same set of environmental conditions and, as a consequence, may be exposed to the same set of environmental constraints. Surprisingly, however, very few studies consider the effects of environmental costs on sexual displays and mate choice simultaneously. We conducted an experiment, manipulating water flow in large flume tanks, to examine how an energetically costly environment might affect the sexual display and mate choice behavior of male and female guppies, Poecilia reticulata. We found that male guppies performed fewer sexual displays and became less choosy, with respect to female size, in the presence of a water current compared to those tested in still water. In contrast to males, female responsive to male displays did not differ between the water current treatments and females exhibited no mate preferences with respect to male size or coloration in either treatment. The results of our study underscore the importance of considering the simultaneous effects of environmental costs on the sexual behaviors of both sexes

The Perils of Picky Eating: Dietary Breadth Is Related to Extinction Risk in Insectivorous Bats

Several recent papers evaluate the relationship between ecological characteristics and extinction risk in bats. These studies report that extinction risk is negatively related to geographic range size and positively related to habitat specialization. Here, we evaluate the hypothesis that extinction risk is also related to dietary specialization in insectivorous vespertilionid bats using both traditional and phylogenetically-controlled analysis of variance. We collected dietary data and The World Conservation Union (IUCN) rankings for 44 Australian, European, and North American bat species. Our results indicate that species of conservation concern (IUCN ranking near threatened or above) are more likely to have a specialized diet than are species of least concern. Additional analyses show that dietary breadth is not correlated to geographic range size or wing morphology, characteristics previously found to correlate with extinction risk. Therefore, there is likely a direct relationship between dietary specialization and extinction risk; however, the large variation in dietary breadth within species of least concern suggests that diet alone cannot explain extinction risk. Our results may have important implications for the development of predictive models of extinction risk and for the assignment of extinction risk to insectivorous bat species. Similar analyses should be conducted on additional bat families to assess the generality of this relationship between niche breadth and extinction risk

Negative phenotypic and genetic associations between copulation duration and longevity in male seed beetles

Reproduction can be costly and is predicted to trade-off against other characters. However, while these trade-offs are well documented for females, there has been less focus on aspects of male reproduction. Furthermore, those studies that have looked at males typically only investigate phenotypic associations, with the underlying genetics often ignored. Here, we report on phenotypic and genetic trade-offs in male reproductive effort in the seed beetle, Callosobruchus maculatus. We find that the duration of a male's first copulation is negatively associated with subsequent male survival, phenotypically and genetically. Our results are consistent with life-history theory and suggest that like females, males trade-off reproductive effort against longevity

The MC1R gene in the guppy (Poecilia reticulata): Genotypic and phenotypic polymorphisms

<p>Abstract</p> <p>Background</p> <p>The guppy (<it>Poecilia reticulata</it>) is an important model organism for studying sexual selection; male guppies have complex and conspicuous pigmentation, and female guppies exhibit preferences for males with specific color spots. Understanding the genetic basis underlying pigmentation variation in the guppy is important for exploring the factors causing the maintenance of color polymorphism in wild populations.</p> <p>Findings</p> <p>We focused on the melanic black pigmentation of guppies, and examined genetic variations in the <it>melanocortin 1 receptor </it>(<it>MC1R</it>) gene because variation in this gene is known to contribute to polymorphism of melanin pigmentation in several animal species. The complete coding sequence of the guppy <it>MC1R </it>gene was determined, and two different <it>MC1R </it>alleles (963 and 969 bp) were found in wild populations. Ornamental strain guppies with a 963-bp <it>MC1R </it>tended to show less black pigmentation than those with a 969-bp <it>MC1R</it>, although the association between <it>MC1R </it>genotype and black pigmentation disappeared in the F₂offspring.</p> <p>Conclusions</p> <p>The guppy <it>MC1R </it>gene showed variation in the five wild Trinidadian populations we examined, and these populations also differed in terms of allele frequencies. We identified a significant association between black pigmentation and <it>MC1R </it>genotype in fish obtained from aquarium shops. However, the results from F₂families suggest that there are other genes that modify the effects of the <it>MC1R </it>gene.</p

Impact Factor: outdated artefact or stepping-stone to journal certification?

A review of Garfield's journal impact factor and its specific implementation as the Thomson Reuters Impact Factor reveals several weaknesses in this commonly-used indicator of journal standing. Key limitations include the mismatch between citing and cited documents, the deceptive display of three decimals that belies the real precision, and the absence of confidence intervals. These are minor issues that are easily amended and should be corrected, but more substantive improvements are needed. There are indications that the scientific community seeks and needs better certification of journal procedures to improve the quality of published science. Comprehensive certification of editorial and review procedures could help ensure adequate procedures to detect duplicate and fraudulent submissions.Comment: 25 pages, 12 figures, 6 table