Genetic Variation of the Long-Legged Flies Phacaspis mitis Complex (Diptera: Dolichopodidae) in Peninsular Thailand Inferred From Three Mitochondrial Genes

Phacaspis (Meuffels and Grootaert 1988) is a true marine dolichopodid fly genus. They are common on the mud flats in the front of mangroves where they deal with extreme conditions. The genus is represented in southern Thailand by Phacaspis mitis (Grootaert and Meuffels 2001) (Diptera: Dolichopodidae). Previous studies have focused on both taxonomy and classification of this genus, but there are a few studies focusing on this species in terms of molecular genetics. The objective of the present study was to investigate genetic variation and phylogenetic relationships of P. mitis using ribosomal DNA subunit 12S, ribosomal DNA subunit 16S, and cytochrome oxidase subunit I of mitochondrial genes. The specimens were collected in six coastal provinces from the Andaman Sea and the Gulf of Thailand. The phylogenetic relationship of combined mitochondrial genes revealed that P. mitis in peninsular Thailand is a monophyletic group that can be divided into two distinct clades. According to the haplotype network, 16 haplotype patterns were observed in P. mitis, but P. mitis was separated into two major haplotype networks. In addition, a positive correlation between genetic distance (FST) and geographical distance (km) was found among the populations of peninsular Thailand. The level of genetic differentiation between populations is influenced by geographic isolation. Moreover, P. mitis arose in late Eocene (35.5 Mya) and it diversified during the Plio-Pleistocene (3.14 Mya). Although, P. mitis is divided into two populations in this study, it is a well-supported monophyletic group.

Infections with the microbe Cardinium in the Dolichopodidae and other Empidoidea

Maternally transmitted reproductive parasites such as Wolbachia and Cardinium can drastically reshape reproduction in their hosts. Beyond skewing sex ratios towards females, these microbes can also cause cytoplasmic incompatibility. Wolbachia probably infects two thirds of insects, but far less is known about the occurrence or action of other bacteria with potentially similar effects. In contrast with the two more widespread reproductive parasites, Wolbachia and Spiroplasma, far less is known of infections with Cardinium (Bacteroidetes) and possible consequences in the Diptera. Here, in an extensive survey, 244 dipteran species from 67 genera belonging to the Dolichopodidae, Empididae, and Hybotidae were assessed for the presence of the microbe Cardinium. Although 130 of the species screened tested positive (ca. 53%), the presence of Cardinium could only be confirmed in 10 species (ca. 4%) based on analysis of sequences. Numerous additional sequences were found to be assignable to known or unknown Bacteroidetes. Considering the known issues concerning specificity of Cardinium primers and the phylogenetic uncertainties surrounding this microbe, the actual prevalence of this symbiont is worthy of further scrutiny. Potential directions for future research on Cardinium-host interactions in Diptera and in general are discussed.

Infections with Wolbachia, Spiroplasma, and Rickettsia in the Dolichopodidae and other Empidoidea

Vertically transmitted reproductive parasites are both extraordinarily widespread and diverse in their effects on their invertebrate hosts. In addition to causing skewed population sex ratios via male-killing or feminization, such bacteria can further cause cytoplasmic incompatibility or parthenogenesis. Previous surveys show that the microbes Wolbachia and Spiroplasma are common in some dipteran families, e.g. Drosophilidae or Scathophagidae, and are known to be heritable symbionts and affect reproduction in the Diptera. However, little is known of Rickettsia infections and detailed surveys targeting other Dipteran families are lacking. Here 329 samples of 247 species of Diptera belonging to the Dolichopodidae, Empididae, and Hybotidae (superfamily Empidoidea) are surveyed for the presence of the endosymbionts Wolbachia, Spiroplasma, and Rickettsia. The superfamily Empidoidea contains numerous species, which have been the targets of intense research concerning reproductive traits involved in sexual selection. 151 of the species (i.e. ca. 61%) screened here, including species from key genera such as Dolichopus, Poecilobothrus or Empis, harboured one or more symbionts. Reproductive parasites are thus also common in the Empidoidae, yet effects on hosts remain unclear. Potential endosymbiont-host interactions in this group would hence be worthy of further investigation.