Testacein

Adaptive radiations provide an opportunity to examine complex evolutionary processes such as ecological specialization and speciation. While a well-resolved phylogenetic hypothesis is critical to completing such studies, the rapid rates of evolution in these groups can impede phylogenetic studies. Here we study the quinaria and testacea species groups of the immigrans-tripunctata radiation of Drosophila, which represent a recent adaptive radiation and are a developing model system for ecological genetics. We were especially interested in understanding host use evolution in these species. In order to infer a phylogenetic hypothesis for this group we sampled loci from both the nuclear genome and the mitochondrial DNA to develop a dataset of 43 protein-coding loci for these two groups along with their close relatives in the immigrans-tripunctata radiation. We used this dataset to examine their evolutionary relationships along with the evolution of feeding behavior. Our analysis recovers strong support for the monophyly of the testacea but not the quinaria group. Results from our ancestral state reconstruction analysis suggests that the ancestor of the testacea and quinaria groups exhibited mushroom-feeding. Within the quinaria group, we infer that transition to vegetative feeding occurred twice, and that this transition did not coincide with a genome-wide change in the rate of protein evolution.

The egg, all three larval instars, and pupa are described for the cucujoid beetle species Monotoma (s. str.) testacea Motschulsky, which develops in decomposing plant matter. Adults and larvae were fed with baker's yeast under laboratory conditions; this food source allowed for successful breeding of several generations. Detailed and illustrated descriptions of all immature stages are given. It is suggested that simple, pointed setae may represent a diagnostic character for Monotoma (s. str.), whereas clavate setae characterize Monotoma (Gyrocecis). Only minor differences in the number and patterns of setae were found between first, second and third larval instars, supporting observations of previous authors. Morphological differences are listed to distinguish between the three larval instars. An arrow-head aggregation of coarse asperities on the frontal region of the L1 larva, lacking in older instars, is hypothesized to be an egg-burster. Only 34-42 days elapsed from egg laying to emergence of the adult; the egg stage lasted 5-6 days; L1 larvae 2-3 days; L2 3-5 days; L3 2-5 days; the immovable prepupal stage 12-13 days; and the pupa 7-10 days. One female laid 1-5 eggs daily, averaging ~1.5 egg per day during her entire life; the total number of eggs in two independent cultures produced by one female accompanied by one male was 57 and 94.

Driving X chromosomes (XD s) bias their own transmission through males by killing Y-bearing gametes. These chromosomes can in theory spread rapidly in populations and cause extinction, but many are found as balanced polymorphisms or as "cryptic" XD s shut down by drive suppressors. The relative likelihood of these outcomes and the evolutionary pathways through which they come about are not well understood. An XD was recently discovered in the mycophagous fly, Drosophila testacea, presenting the opportunity to compare this XD with the well-studied XD of its sister species, Drosophila neotestacea. Comparing features of independently evolved XD s in young sister species is a promising avenue towards understanding how XD s and their counteracting forces change over time. In contrast to the XD of D. neotestacea, we find that the XD of D. testacea is old, with its origin predating the radiation of three species: D. testacea, D. neotestacea and their shared sister species, Drosophila orientacea. Motivated by the suggestion that older XD s should be more deleterious to carriers, we assessed the effect of the XD on both male and female fertility. Unlike what is known from D. neotestacea, we found a strong fitness cost in females homozygous for the XD in D. testacea: a large proportion of homozygous females failed to produce offspring after being housed with males for several days. Our male fertility experiments show that although XD male fertility is lower under sperm-depleting conditions, XD males have comparable fertility to males carrying a standard X chromosome under a free-mating regime, which may better approximate conditions in wild populations of D. testacea. Lastly, we demonstrate the presence of autosomal suppression of X chromosome drive. Our results provide support for a model of XD evolution where the dynamics of young XD s are governed by fitness consequences in males, whereas in older XD systems, both suppression and fitness consequences in females likely supersede male fitness costs.