Exaggerated sexual traits, such as ornaments and courtship displays, are crucial for mate acquisition in many species and are often subject to directional runaway selection. However, in the face of high predation risk, natural selection can result in a reduction of conspicuous precopulatory displays to avoid detection by potential predators. Sexual selection may then favour increased investment in inconspicuous postcopulatory traits. Here, we investigated the transgenerational effects of predation on precopulatory male courtship and postcopulatory sexual traits (testes size, sperm length) in a dung fly, Sepsis punctum (Sepsidae). Behavioural assays prior to selection document a marked decrease in male courtship displays in the presence of a predator, the Asian Ant Mantis (Odontomantis planiceps). However, after ten generations of experimental evolution, flies exhibited a marked increase in courtship, both in the absence and presence of a predator. Additionally, under sustained predation pressure, male and female body size decreased but male postcopulatory traits were not significantly affected. These results suggest that precopulatory courtship can be under strong sexual selection even in the face of predation pressure. Larger flies were more susceptible to predation, and there could be canalisation of postcopulatory traits that are crucial for fertilisation.

Meroplius fukuharai is an important sanitary and ecological resource insect. We sequenced and annotated the mitogenome of Meroplius fukuharai which is the first representative of the genus Meroplius with nearly complete mitochondrial data. This mitogenome is 14,803 bp long, which consists of 22 transfer RNA genes, 13 protein-coding genes (PCGs), and two ribosomal RNA genes. All genes have a conservational arrangement with other published species of Sepsidae. Our results also supported the monophyly of Sepsidae, and the genus Meroplius is more closely related to genus Sepsis, Microsepsis, and Archisepsis.

AbstractThe black scavenger fly Sepsis thoracica exhibits polyphenic development resulting in alternate small black and large amber male morphs. Although the behavior, ecology, and physiology of both morphs are being scrutinized, the evolutionary origins of the nutritional polyphenism remain poorly understood. I here use a comparative approach to study variation in the degree of melanization of the forefemur-a secondary sexual trait. Melanization showed nutritional plasticity in all species, and character mapping suggests polyphenic development to represent the ancestral character state that was lost repeatedly. That is, interspecific variation among the studied species is mainly caused by the loss and not the gain of polyphenic development. Coevolution between male melanization and mating system differences further implicates sexual selection in the evolution of male melanization. These findings highlight the usefulness of comparative and natural history data in shedding new light on the evolution of phenotypic variation.

The sepsid fly Sepsis monostigma belongs to the genus Sepsis of Sepsidae. We sequenced and annotated the mitogenome of S. monostigma which as the first representative of genus Sepsis with nearly complete mitochondrial data. This mitogenome is 14,887bp long, which contains of 22 transfer RNA genes, 13 protein coding genes (PCGs) and 2 ribosomal RNA genes and a part of the AT control region. ML phylogenetic outcome strongly supported the monophyly of Sepsidae, and the family Sepsidae is more close to the family Heleomyzidae. It also indicated that the genus Sepsis is the sister group to Nemopoda, and the genus Archisepsis is the sister group to Microsepsis.

Sexual selection is generally held responsible for the exceptional diversity in secondary sexual traits in animals. Mating system evolution is therefore expected to profoundly affect the covariation between secondary sexual traits and mating success. Whereas there is such evidence at the interspecific level, data within species remain scarce. We here investigate sexual selection acting on the exaggerated male fore femur and the male wing in the common and widespread dung flies Sepsis punctum and S. neocynipsea (Diptera: Sepsidae). Both species exhibit intraspecific differences in mating systems and variation in sexual size dimorphism (SSD) across continents that correlates with the extent of male-male competition. We predicted that populations subject to increased male-male competition will experience stronger directional selection on the sexually dimorphic male foreleg. Our results suggest that fore femur size, width and shape were indeed positively associated with mating success in populations with male-biased SSD in both species, which was not evident in conspecific populations with female-biased SSD. However, this was also the case for wing size and shape, a trait often assumed to be primarily under natural selection. After correcting for selection on overall body size by accounting for allometric scaling, we found little evidence for independent selection on any of these size or shape traits in legs or wings, irrespective of the mating system. Sexual dimorphism and (foreleg) trait exaggeration is therefore unlikely to be driven by direct precopulatory sexual selection, but more so by selection on overall size or possibly selection on allometric scaling.

Thermal performance curves (TPCs) have been estimated in multiple ectotherm species to understand their thermal plasticity and adaptation and to predict the effect of global warming. However, TPCs are typically assessed under constant temperature regimes, so their reliability for predicting thermal responses in the wild where temperature fluctuates diurnally and seasonally remains poorly documented. Here, we use distant latitudinal populations of five species of sepsid flies (Diptera: Sepsidae) from the temperate region (Europe, North Africa, North America) to compare estimates derived from constant TPCs with observed development rate under fluctuating temperatures in laboratory and field conditions. TPCs changed across gradients in that flies originating from higher latitudes showed accelerated development at higher temperatures, an adaptive response. TPCs were then used to predict development rates observed under fluctuating temperatures; these predictions were relatively accurate in the laboratory but not the field. Interestingly, the precision of TPC predictions depended not only on the resolution of temperature data, with daily and overall temperature summing performing better than hourly temperature summing, but also on the frequency of temperatures falling below the estimated critical minimum temperature. Hourly temperature resolution most strongly underestimated actual development rates, because flies apparently either did not stop growing when temperatures dropped below this threshold, or they sped up their growth when the temperature rose again, thus most severely reflecting this error. We conclude that when flies do not encounter cold temperatures, TPC predictions based on constant temperatures can accurately reflect performance under fluctuating temperatures if adequately adjusted for nonlinearities, but when encountering cold temperatures, this method is more error-prone. Our study emphasizes the importance of the resolution of temperature data and cold temperatures in shaping thermal reaction norms.

Sexual selection can displace traits acting as ornaments or armaments from their viability optimum in one sex, ultimately giving rise to sexual dimorphism. The degree of dimorphism should not only mirror the strength of sexual selection but also the net viability costs of trait maintenance at equilibrium. As the ability of organisms to bear exaggerated traits will depend on their condition, more sexually dimorphic traits should also exhibit greater sex differences in condition dependence. While this has been demonstrated among traits within species, similar patterns are expected across the phylogeny. We investigated this prediction within and across 11 (sub)species of sepsid flies with varying mating systems. When estimating condition dependence for seven sexual and nonsexual traits that vary in their sexual dimorphism, we not only found a positive relationship between the sex difference in allometric slopes (our measure of condition dependence) and relative trait exaggeration within species but also across species for those traits expected to be under sexual selection. Species with more pronounced male aggression further had relatively larger and more condition-dependent male fore- and midlegs. Our comparative study suggests a common genetic/developmental basis of sexual dimorphism and sex-specific plasticity that evolves across the phylogeny-and that the evolution of size consistently alters scaling relationships and thus contributes to the allometric variation of sexual armaments or ornaments in animals.

The males of some sepsid species (Sepsidae: Diptera) have abdominal appendages that are remarkable in several ways. They are sexually dimorphic, have a complex evolutionary history of gain and loss, and can be jointed and thus highly mobile. The sternite brushes are used extensively in complex courtship behaviors that differ considerably between species and during mating. The abdominal appendages have a novel developmental pathway developing from histoblast nests rather than imaginal discs.
We focus on the evolution of cell number, nest area, and segment length in both sexes to understand how this tissue relates to the formation of novel abdominal appendages. We map histoblast nest size of wandering-phase larvae of 17 species across 10 genera to a phylogenetic tree of Sepsidae and demonstrate that abdominal appendages require significant increases of histoblast nest size and cell number in most species while one species produces small appendages even without such modifications. In species with particularly large appendages, not only the nests on the fourth, but nests in neighboring segments are enlarged (Themira biloba, Themira putris). The loss of abdominal appendages corresponds to the loss of an enlarged fourth histoblast nest, although one species showed an exception to this pattern. One species that constitutes an independent origin of abdominal appendages (Perochaeta dikowi) uses an unusual developmental mechanism in that the histoblast nest sizes are not sexually dimorphic.
The surprisingly high diversity in histoblast size and degree of sexual dimorphism suggests that the developmental mechanism used for abdominal appendage formation in sepsids is highly adaptable. The presence of appendages usually correlate with increased histoblast cell number and in most cases appendage loss results in a return to ancestral histoblast morphology. However, we also identify several exceptions that indicate the abdominal appendages have a malleable developmental origin that is responsive to selection.

Ivermectin is a veterinary pharmaceutical widely applied against parasites of livestock. Being effective against pests, it is also known to have lethal and sublethal effects on non-target organisms. While considerable research demonstrates the impact of ivermectin residues in livestock dung on the development and survival of dung feeding insect larvae, surprisingly little is known about its fitness effects on adults. We tested the impact of ivermectin on the survival of adult sepsid dung fly species (Diptera: Sepsidae) in the laboratory, using an ecologically relevant and realistic range of 69-1978 µg ivermectin/kg wet dung, and compared the sensitivities of larvae and adults in a phylogenetic framework. For one representative, relatively insensitive species, Sepsis punctum, we further investigated effects of ivermectin on female fecundity and male fertility. Moreover, we tested whether females can differentiate between ivermectin-spiked and non-contaminated dung in the wild. Adult sepsid flies exposed to ivermectin suffered increased mortality, whereby closely related species varied strongly in their sensitivity. Adult susceptibility to the drug correlated with larval susceptibility, showing a phylogenetic signal and demonstrating systemic variation in ivermectin sensitivity. Exposure of S. punctum females to even low concentrations of ivermectin lowered the number of eggs laid, while treatment of males reduced egg-to-adult offspring survival, presumably via impairment of sperm quality or quantity. The fitness impact was amplified when both parents were exposed. Lastly, sepsid flies did not discriminate against ivermectin-spiked dung in the field. Treatment of livestock with avermectins may thus have even more far-reaching sublethal ecological consequences than currently assumed via effects on adult dung-feeding insects.

New species from well-studied taxa such as Sepsidae (Diptera) are rarely described from localities that have been extensively explored and one may think that New York City belongs to this category. Yet, a new species of Themira (Diptera: Sepsidae) was recently discovered which is currently only known to reside in two of New York City\'s largest urban parks. Finding a new species of Themira in these parks was all the more surprising because the genus was revised in 1998 and is not particularly species-rich (13 species). Its status is confirmed as a new species based on morphology, DNA sequences, and reproductive isolation tests with a closely related species, and is described as Themira lohmanus Ang, sp. n. The species breeds on waterfowl dung and it is hypothesized that this makes the species rare in natural environments. However, it thrives in urban parks where the public feeds ducks and geese. The mating behavior of Themira lohmanus was recorded and is similar to the behavior of its closest relative T. biloba.