Alcohol dehydrogenase polymorphism in barrel cactus populations of Drosophila mojavensis

Starch gel electrophoresis revealed that the alcohol dehydrogenase (ADH-2) locus was polymorphic in two populations (from Agua Caliente, California and the Grand Canyon, Arizona) of cactophilic Drosophila mojavensis that utilize barrel cactus (Ferocactus acanthodes) as a host plant. Electromorphs representing products of a slow (S) and a fast (F) allele were found in adult flies. The frequency of the slow allele was 0.448 in flies from Agua Caliente and 0.659 in flies from the Grand Canyon. These frequencies were intermediate to those of the low (Baja California peninsula, Mexico) and high (Sonora, Mexico and southern Arizona) frequency Adh-2^S populations of D. mojavensis that utilize different species of host cacti.     

"Cost" of virginity in wild Drosophila melanogaster females

Laboratory studies have revealed a significant "cost of mating" to Drosophila melanogaster females in the form of reduced longevity. The effect is attributable to nonsperm components of the ejaculate. Female D. melanogaster are known to mate up to six times in nature, and given that they do not typically remate daily, it raises the question as to the extent to which the longevity of wild mated females is reduced. Here I addressed this question by comparing the longevity of wild virgin females, collected as they emerged from rotting fruit, to the longevity of randomly collected mature females at the same site. Because the randomly collected females all were inseminated and were fully pigmented at the time of collection, they already were older than the virgins when the experiment began. Contrary to expectations from laboratory studies, the older, mated females lived significantly longer than the virgins. Rather than a "cost of mating," there appears to be a "cost of virginity" to female D. melanogaster in the wild.     

The 19 genomes of Drosophila: a BAC library resource for genus-wide and genome-scale comparative evolutionary research

The genus Drosophila has been the subject of intense comparative phylogenomics characterization to provide insights into genome evolution under diverse biological and ecological contexts and to functionally annotate the Drosophila melanogaster genome, a model system for animal and insect genetics. Recent sequencing of 11 additional Drosophila species from various divergence points of the genus is a first step in this direction. However, to fully reap the benefits of this resource, the Drosophila community is faced with two critical needs: i.e., the expansion of genomic resources from a much broader range of phylogenetic diversity and the development of additional resources to aid in finishing the existing draft genomes. To address these needs, we report the first synthesis of a comprehensive set of bacterial artificial chromosome (BAC) resources for 19 Drosophila species from all three subgenera. Ten libraries were derived from the exact source used to generate 10 of the 12 draft genomes, while the rest were generated from a strategically selected set of species on the basis of salient ecological and life history features and their phylogenetic positions. The majority of the new species have at least one sequenced reference genome for immediate comparative benefit. This 19-BAC library set was rigorously characterized and shown to have large insert sizes (125-168 kb), low nonrecombinant clone content (0.3-5.3%), and deep coverage (9.1-42.9×). Further, we demonstrated the utility of this BAC resource for generating physical maps of targeted loci, refining draft sequence assemblies and identifying potential genomic rearrangements across the phylogeny.     

Population genetics and recent colonization history of the invasive drosophilid Zaprionus indianus in Mexico and Central America

Zaprionus indianus, also known as the African fig fly, is an invasive pest of a variety of commercial and native fruit. The species was first reported in Brazil in 1999, but has established itself in much of the New World within the last 10–15 years. We used nucleotide sequences from a segment of the mitochondrial cytochrome c oxidase subunit I (COI) gene to examine haplotype relationships, population structure, and infer the colonization history of Z. indianus in Mexico and Panama. Construction of a haplotype network showed that six COI haplotypes, obtained from flies collected at six localities in Mexico and one in Panama, clustered into three distinct clades. Clade composition was generally consistent in flies from Panama to northwestern Mexico, and analysis of molecular variance indicated no significant structure among populations. Three of the six haplotypes from Mexico and Panama were identical to previously reported haplotypes from Brazil. None of the six haplotypes, however, were shared with previously reported haplotypes from potential source populations in the Old World. The results of our genetic analysis suggest that the invasion of Z. indianus into Central America and Mexico most probably includes a northward migration of individuals from Brazil, with the possibility of at least one additional introduction of Z. indianus to the New World. Additional sequence data from potential source populations in the Old World will be required to confidently determine the number of introductions of Z. indianus into the New World, and to identify the geographic source.     

Dispersal in cactophilic Drosophila

Three species of Drosophila each breed in necrotic tissue of specific columnar cacti endemic to the Sonoran Desert. Drosophila pachea breeds in senita ( Lophocereus schottii) , D. nigrospiracula breeds in saguaro ( Carnegiea gigantea ) or cardón ( Pachycereus pringlei ), and D. mojavensis uses organ pipe ( Stenocereus thurberi ) in Sonora, Mexico and southern Arizona. Patches of these three host cacti have very different spatial distributions, with those of senita being quite frequent and close together, while those of the other hosts are much father apart. Testing all three species simultaneously, we used capture-mark-release-recapture methods to ask if dispersal differed in these species and if differences were those predicted by the spatial availability of the host patches. D. pachea dispersed the shortest distance in all experiments. Furthermore, D. pachea was the only species showing sex-biased dispersal, with male flies exhibiting the greater propensity to disperse. The observations suggest that across similar spatial scales, D. pachea should show greater population genetic structure than the other two species, and that mitochondrial DNA, because of its maternal inheritance, might show greater evidence of structure than nuclear markers.     

Phylogenetic relationships of leopard frogs (Rana pipiens complex) from an isolated coastal mountain range in southern Sonora, Mexico

Mitochondrial DNA sequence data from the control region and 12S rRNA in leopard frogs from the Sierra El Aguaje of southern Sonora, Mexico, together with GenBank sequences, were used to infer taxonomic identity and provide phylogenetic hypotheses for relationships with other members of the Rana pipiens complex. We show that frogs from the Sierra El Aguaje belong to the Rana berlandieri subgroup, or Scurrilirana clade, of the R. pipiens group, and are most closely related to Rana magnaocularis from Nayarit, Mexico. We also provide further evidence that Rana magnaocularis and R. yavapaiensis are close relatives.     

Mating system evolution in sperm-heteromorphic Drosophila

In Drosophila species of the obscura group, males exhibit sperm-heteromorphism, simultaneously producing both long sperm, capable of fertilization, and short sperm that are not. The production of multiple sperm types calls into question whether mating system correlates, such as sperm length and number trade-offs and female remating behavior, are the same as previously described in sperm-monomorphic systems. We examine three obscura group species, D. pseudoobscura, D. persimilis, and D. affinis that differ significantly in the lengths of their long fertilizing sperm, to test predictions about the relationship between sperm length and four mating system characters: male age at sexual maturity; sperm number; female remating; and male reproductive output. In D. affinis, where males produce the longest fertilizing sperm, their sexual maturity is delayed and they produce fewer long sperm compared to the other two species, as predicted if long sperm are costly to produce. Female D. affinis, although they receive fewer sperm than females of the other two species, do not remate more frequently or produce fewer progeny from a single mating. Different responses between sperm-heteromorphic and sperm-monomorphic systems underscore the complex nature of the coevolution between male and female mating system characters.     

A comparative investigation of the mating system of Drosophila hydei

Drosophila hydei mating system characteristics were studied and compared to what has been observed for two other Drosophila species. Hydei females will copulate when they are 3 days old, while males do not exhibit courtship behaviour until they are 9 days old. Unlike any other Drosophila, D. hydei females will re-mate as often as four times in one morning. However, re-mating in the same morning does not increase the number of progeny a female produces. Male D. hydei appear to deal with the continual receptivity of females and the pressures of sperm competition by passing less material to any given female but maintaining a constant level of fertility across numerous successive copulations. D. hydei is a cosmopolitan species which utilizes a wide variety of resources. As in D. melanogaster, another cosmopolitan species which is not closely related to it, male success appears to be dependent upon genetic quality only. This pattern differs from that observed in its relative D. mojavensis, a cactiphilic species endomic to the Sonoran desert, in which males contribute material benefits to females in their ejaculate.     

Desiccation resistance in four Drosophila species: sex and population effects

Desiccation resistance and body mass were measured in multiple populations of each of four species of Drosophila: two desert endemic species (D. nigrospiracula and D. mojavensis), and two with more widespread distributions (D. melanogaster and D. pseudoobscura). While flies from the desert species were more desiccation tolerant, there was, in certain cases, significant variation in desiccation resistance among populations of the same species. A significant difference in desiccation resistance was observed between the sexes, females were more resistant than males, but this relationship was reversed when taking into account body mass differences between the sexes. The degree of observed within-species variability demonstrates that studies focusing upon differences between species can produce different conclusions if they rely on observations for only single populations of a given species. Our data also suggest the existence of multiple mechanisms for desiccation resistance.