Meiotic drive systems are associated with low-frequency chromosomal inversions. These are expected to accumulate deleterious mutations due to reduced recombination and low effective population size. We test this prediction using the 'sex-ratio' (SR) meiotic drive system of the Malaysian stalk-eyed fly Teleopsis dalmanni. SR is associated with a large inversion (or inversions) on the X chromosome. In particular, we study eyespan in males carrying the SR chromosome, as this trait is a highly exaggerated, sexually dimorphic trait, known to have heightened condition-dependent expression. Larvae were raised in low and high larval food stress environments. SR males showed reduced eyespan under the low and high stress treatments, but there was no evidence of a condition-dependent decrease in eyespan under high stress. Similar but more complex patterns were observed for female eyespan, with evidence of additivity under low stress and heterosis under high stress. These results do not support the hypothesis that reduced sexual ornament size in meiotic drive males is due to a condition-dependent response to the putative increase in mutation load. Instead, reduced eyespan likely reflects compensatory resource allocation to different traits in response to drive-mediated destruction of sperm.
The widespread nominal black fly Simulium (Simulium) rufibasis Brunetti was reexamined morphologically, chromosomally, and molecularly to determine the status of populations in Japan and Korea with respect to S. rufibasis from the type locality in India and to all other known species in the S. (S.) tuberosum species-group. Morphological comparisons established that the species previously known as S. rufibasis in Japan and Korea is distinct from all other species. Consequently, it was described and illustrated as a new species, Simulium (S.) yamatoense. Simulium yokotense Shiraki, formerly a synonym of S. rufibasis, was morphologically reevaluated and considered a species unplaced to species-group in the subgenus Simulium. Chromosomal analyses of S. yamatoense sp. nov. demonstrated that it is unique among all cytologically known species of the S. tuberosum group and is the sister species of the Taiwanese species tentatively known as S. (S.) arisanum Shiraki. Populations of S. yamatoense sp. nov. included two cytoforms, based on the sex chromosomes. Cytoform A, including topotypical representatives, was found in Kyushu, Japan, whereas cytoform B was found in Korea and Honshu, Japan. Molecular analysis based on the COI mitochondrial gene generally corroborated morphological and chromosomal data that S. yamatoense sp. nov. is a distinct species and, like the chromosomal data, indicate that it is most closely related to S. arisanum, with interspecific genetic distance of 2.92-4.63%.
Southeast Asian populations of the fruit fly Drosophila melanogaster differ from ancestral African and derived European populations by several morphological characteristics. It has been argued that this morphological differentiation could be the result of an early colonization of Southeast Asia that predated the migration of D. melanogaster to Europe after the last glacial period (around 10,000 years ago). To investigate the colonization process of Southeast Asia, we collected nucleotide polymorphism data for more than 200 X-linked fragments and 50 autosomal loci from a population of Malaysia. We analyzed this new single nucleotide polymorphism data set jointly with already existing data from an African and a European population by employing an Approximate Bayesian Computation approach. By contrasting different demographic models of these three populations, we do not find any evidence for an early divergence between the African and the Asian populations. Rather, we show that Asian and European populations of D. melanogaster share a non-African most recent common ancestor that existed about 2,500 years ago.