Kim van der Linde

Proximate Causes of Rensch’s Rule: Does Sexual Size Dimorphism in Arthropods Result from Sex Differences in Development Time?

A prominent interspecific pattern of sexual size dimorphism (SSD) is Rensch’s rule, according to which male body size is more variable or evolutionarily divergent than female body size. Assuming equal growth rates of males and females, SSD would be entirely mediated, and Rensch’s rule proximately caused, by sexual differences in development times, or sexual bimaturism (SBM), with the larger sex developing for a proportionately longer time. Only a subset of the seven arthropod groups investigated in this study exhibits Rensch’s rule. Furthermore, we found only a weak positive relationship between SSD and SBM overall, suggesting that growth rate differences between the sexes are more important than development time differences in proximately mediating SSD in a wide but by no means comprehensive range of arthropod taxa. Except when protandry is of selective advantage (as in many butterflies, Hymenoptera, and spiders), male development time was equal to (in water striders and beetles) or even longer than (in drosophilid and sepsid flies) that of females. Because all taxa show female‐biased SSD, this implies faster growth of females in general, a pattern markedly different from that of primates and birds (analyzed here for comparison). We discuss three potential explanations for this pattern based on life‐history trade‐offs and sexual selection.

A supermatrix-based molecular phylogeny of the family Drosophilidae.

The genus Drosophila is diverse and heterogeneous and contains a large number of easy-to-rear species, so it is an attractive subject for comparative studies. The ability to perform such studies is currently compromised by the lack of a comprehensive phylogeny for Drosophila and related genera. The genus Drosophila as currently defined is known to be paraphyletic with respect to several other genera, but considerable uncertainty remains about other aspects of the phylogeny. Here, we estimate a phylogeny for 176 drosophilid (12 genera) and four non-drosophilid species, using gene sequences for up to 13 different genes per species (average: 4333 bp, five genes per species). This is the most extensive set of molecular data on drosophilids yet analysed. Phylogenetic analyses were conducted with maximum-likelihood (ML) and Bayesian approaches. Our analysis confirms that the genus Drosophila is paraphyletic with 100% support in the Bayesian analysis and 90% bootstrap support in the ML analysis. The subgenus Sophophora, which includes Drosophila melanogaster, is the sister clade of all the other subgenera as well as of most species of six other genera. This sister clade contains two large, well-supported subclades. The first subclade contains the Hawaiian Drosophila, the genus Scaptomyza, and the virilis-repleta radiation. The second contains the immigrans-tripunctata radiation as well as the genera Hirtodrosophila (except Hirtodrosophila duncani), Mycodrosophila, Zaprionus and Liodrosophila. We argue that these results support a taxonomic revision of the genus Drosophila.

FIRST RECORDS OF ZAPRIONUS INDIANUS (DIPTERA: DROSOPHILIDAE), A PEST SPECIES ON COMMERCIAL FRUITS FROM PANAMA AND THE UNITED STATES OF AMERICA

Zaprionus indianus Gupta 1970 (Diptera: Drosophilidae) is native to Africa, the Middle East, and southern Eurasia (Chassagnard & Kraaijeveld 1991; Baichli 1999-2005). It was first found in the Americas in 1999, when it was reported from Sao Paulo, Brazil (Vilela 1999). Since then, it has spread rapidly through Brazil (Santos et al. 2003; Tidon et al. 2003; Ledo & Tidon 2004; da Silva et al. 2005) and Uruguay (Goni et al. 2001, 2002) and has been predicted to reach the USA in the near future (David et al. 2006). Here we report the first records of Z. indianus from Panama and the USA. On 6 and 7 Oct 2003, DH collected several individuals of Z. indianus on Isla Contadora, Panama. KH reared several individuals of Zaprionus (Steck 2005) from fruits of longan, Dimocarpus longan Lour., and Barbados cherry, Malpighia emarginata Sess6 & Moc. ex DC., collected on 26 Jul 2005 in St. Lucie Co., Florida. Dr. C. Ribeiro Vilela confirmed the identification as Z. indianus.

A supertree analysis and literature review of the genus Drosophila and closely related genera (Diptera, Drosophilidae).

In the 17 years since the last familywide taxonomic analysis of the Drosophilidae, many studies dealing with a limited number of species or groups have been published. Most of these studies were based on molecular data, but morphological and chromosomal data also continue to be accumulated. Here, we review more than 120 recent studies and use many of those in a supertree analysis to construct a new phylogenetic hypothesis for the genus Drosophila and related genera. Our knowledge about the phylogeny of the genus D rosophila and related genera has greatly improved over the past two decades, and many clades are now firmly supported by many independent studies. The genus Drosophila is paraphyletic and comprises four major clades interspersed with at least five other genera, warranting a revision of the genus. Despite this progress, many relationships remain unresolved. Much phylogenetic work on this important family remains to be done.

Complex constraints on allometry revealed by artificial selection on the wing of Drosophila melanogaster

Significance Many traits scale precisely with size, but it is unknown whether this is due to selection for optimal function or due to evolutionary constraint. We use artificial selection to demonstrate that wing-shape scaling in fruit flies can respond to selection. This evolved response in scaling was lost during a few generations after selection ended, but other selected changes in wing shape persisted. Shape–size scaling in fly wings is therefore evolvable, but adaptation is apparently constrained by selection that may not be on wings. This may explain why scaling relationships are often evolutionarily conserved. Precise exponential scaling with size is a fundamental aspect of phenotypic variation. These allometric power laws are often invariant across taxa and have long been hypothesized to reflect developmental constraints. Here we test this hypothesis by investigating the evolutionary potential of an allometric scaling relationship in drosophilid wing shape that is nearly invariant across 111 species separated by at least 50 million years of evolution. In only 26 generations of artificial selection in a population of Drosophila melanogaster, we were able to drive the allometric slope to the outer range of those found among the 111 sampled species. This response was rapidly lost when selection was suspended. Only a small proportion of this reversal could be explained by breakup of linkage disequilibrium, and direct selection on wing shape is also unlikely to explain the reversal, because the more divergent wing shapes produced by selection on the allometric intercept did not revert. We hypothesize that the reversal was instead caused by internal selection arising from pleiotropic links to unknown traits. Our results also suggest that the observed selection response in the allometric slope was due to a component expressed late in larval development and that variation in earlier development did not respond to selection. Together, these results are consistent with a role for pleiotropic constraints in explaining the remarkable evolutionary stability of allometric scaling.

Inferring the Nature of Allometry from Geometric Data

The form of an organism is the combination of its size and its shape. For a sample of forms, biologists wish to characterize both mean form and the variation in form. For geometric data, where form is characterized as the spatial locations of homologous points, the first step in analysis superimposes the forms, which requires an assumption about what measure of size is appropriate. Geometric morphometrics adopts centroid size as the natural measure of size, and assumes that variation around the mean form is isometric with size. These assumptions limit the interpretation of the resulting estimates of mean and variance in form. We illustrate these problems using allometric variation in shape. We show that superimposition based on subsets of relatively isometric points can yield superior inferences about the overall pattern of variation. We propose and demonstrate two superimposition techniques based on this idea. In subset superimposition, landmarks are progressively discarded from the data used for superimposition if they result in significant decreases in the variation among the remaining landmarks. In outline superimposition, regularly distributed pseudolandmarks on the continuous outline of a form are used as the basis for superimposition of the landmarks contained within it. Simulations show that these techniques can result in dramatic improvements in the accuracy of estimated variance-covariance matrices among landmarks when our assumptions are roughly satisfied. The pattern of variation inferred by means of our superimposition techniques can be quite different from that recovered from full generalized Procrustes superimposition. The pattern of shape variation in the wings of drosophilid flies appears to meet these assumptions. Adoption of superimposition procedures that incorporate biological assumptions about the nature of size and of the variation in shape can dramatically improve the ability to infer the pattern of variation in geometric morphometric data.

Mutation predicts 40 million years of fly wing evolution

Mutation enables evolution, but the idea that adaptation is also shaped by mutational variation is controversial. Simple evolutionary hypotheses predict such a relationship if the supply of mutations constrains evolution, but it is not clear that constraints exist, and, even if they do, they may be overcome by long-term natural selection. Quantification of the relationship between mutation and phenotypic divergence among species will help to resolve these issues. Here we use precise data on over 50,000 Drosophilid fly wings to demonstrate unexpectedly strong positive relationships between variation produced by mutation, standing genetic variation, and the rate of evolution over the last 40 million years. Our results are inconsistent with simple constraint hypotheses because the rate of evolution is very low relative to what both mutational and standing variation could allow. In principle, the constraint hypothesis could be rescued if the vast majority of mutations are so deleterious that they cannot contribute to evolution, but this also requires the implausible assumption that deleterious mutations have the same pattern of effects as potentially advantageous ones. Our evidence for a strong relationship between mutation and divergence in a slowly evolving structure challenges the existing models of mutation in evolution.

The fruit fly formerly know as Drosophila

The famous fly is about to be renamed – and thats a bad idea says ecologist Kim van der Linde, while geneticist Amir Yassin says change is overdue