Abstract:We here argue that data from comparative studies of genome size and karyotypes provide important information for planning comparative research on genome evolution. We document for 39 species of sepsids that there is a four-fold difference in genome size (151-618 Mbp). Mapping genome sizes onto a phylogenetic hypothesis identifies that this range is the result of five genome expansions and four genome contractions that we here define as changes in genome size of more than 50 Mbp. We then generate karyotype data… Show more
“…The species sampled for histoblast analysis represent one primary gain and three independent losses of the abdominal appendage as well as Orygma luctuosum , a sister group to the remaining sepsid species which lacks abdominal appendages. The pattern of gains and losses was inferred from a phylogeny with more taxa [ 18 ] Fig. 2 Abdominal view of adult flies of the sampled species.…”
Section: Resultsmentioning
confidence: 99%
“…In order to place the cell number in a phylogenetic context, we mapped cell number values onto the sepsid phylogeny. Using an existing sepsid phylogeny created using multiple genetic markers [ 18 ] we created a phylogenetic tree of the study species with colors representing the degree of sexual dimorphism in the mean 4th segment histoblast cell number with cooler colors representing increased dimorphism in the histoblast nests (Fig. 8 ).…”
Section: Resultsmentioning
confidence: 99%
“…The most recent phylogeny of the Sepsidae supports a single gain of abdominal appendages and multiple independent losses [ 18 ]. Species were sampled across the Sepsidae to get multiple examples of species with and without abdominal appendages (Figs.…”
BackgroundThe 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.ResultsWe 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.ConclusionsThe 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.Electronic supplementary materialThe online version of this article (10.1186/s12862-018-1265-3) contains supplementary material, which is available to authorized users.
“…The species sampled for histoblast analysis represent one primary gain and three independent losses of the abdominal appendage as well as Orygma luctuosum , a sister group to the remaining sepsid species which lacks abdominal appendages. The pattern of gains and losses was inferred from a phylogeny with more taxa [ 18 ] Fig. 2 Abdominal view of adult flies of the sampled species.…”
Section: Resultsmentioning
confidence: 99%
“…In order to place the cell number in a phylogenetic context, we mapped cell number values onto the sepsid phylogeny. Using an existing sepsid phylogeny created using multiple genetic markers [ 18 ] we created a phylogenetic tree of the study species with colors representing the degree of sexual dimorphism in the mean 4th segment histoblast cell number with cooler colors representing increased dimorphism in the histoblast nests (Fig. 8 ).…”
Section: Resultsmentioning
confidence: 99%
“…The most recent phylogeny of the Sepsidae supports a single gain of abdominal appendages and multiple independent losses [ 18 ]. Species were sampled across the Sepsidae to get multiple examples of species with and without abdominal appendages (Figs.…”
BackgroundThe 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.ResultsWe 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.ConclusionsThe 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.Electronic supplementary materialThe online version of this article (10.1186/s12862-018-1265-3) contains supplementary material, which is available to authorized users.
“…Sepsid flies (Diptera: Sepsidae) have become a model group for the study of sexual selection and ecological adaptation (Baur et al, 2020;Blanckenhorn, 1999;Blanckenhorn et al, 2000;Eberhard, 1999;Parker, 1972a,b;Puniamoorthy et al, 2009;Pont & Meier, 2002;Rohner et al, 2015;Rohner, Blanckenhorn, & Puniamoorthy, 2016;Ward, 1983;Ward, Hemmi, & Rösli, 1992). The phylogeny of sepsid flies is well resolved (Su et al, 2008(Su et al, , 2016 and entails multiple pairs of closely related species that occupy similar ecological niches. These species pairs provide excellent opportunities to study the genomic consequences of hybridization and introgression during early stages of speciation.…”
Section: Introductionmentioning
confidence: 99%
“…. (A) Species phylogeny inferred from alignments of nucleotide sequences at the cytochrome oxidase subunit II (CO-II) mitochondrial locus (Genbank sequences fromSu et al, 2016) with the Neighbor-Joining method implemented in CLC Main Workbench (v. 8.1.2; https:// https://www.qiagenbioinformatics.com/products/clc-main-workbench/). The tree topology is consistent with the phylogeny presented bySu et al's (2016) combined phylogenetic analysis of multiple nuclear and mitochondrial markers.…”
Interspecific gene flow by hybridization may weaken species barriers and adaptive divergence, but also initiate reinforcement of reproductive isolation trough natural and sexual selection. The extent and consequences of interspecific gene flow in natural systems remain poorly understood. To assess genome-wide patterns of gene flow between the two closely related European dung fly species Sepsis cynipsea and Sepsis neocynipsea (Diptera: Sepsidae), we analyzed whole-genome resequencing data from pooled males of laboratory and field populations by means of the ABBA-BABA test. We contrasted genome-wide variation in DNA sequence differences between samples from sympatric populations of these two species in France and Switzerland with that of interspecific pairs of samples involving allopatric populations from Estonia and Italy. In the French Cevennes, we detected a relative excess of sequence identity suggesting interspecific gene flow in sympatry. In contrast, at two sites in Switzerland we observed a relative depletion of sequence identity compatible with reinforcement of species boundaries in sympatry. Our results suggest that the species boundaries between S. cynipsea and S. neocynipsea in Europe are not fixed but depend on the eco-geographic context.
The extent of interspecific gene flow and its consequences for the initiation, maintenance, and breakdown of species barriers in natural systems remain poorly understood. Interspecific gene flow by hybridization may weaken adaptive divergence, but can be overcome by selection against hybrids, which may ultimately promote reinforcement. An informative step towards understanding the role of gene flow during speciation is to describe patterns of past gene flow among extant species. We investigate signals of admixture between allopatric and sympatric populations of the two closely related European dung fly species Sepsis cynipsea and S. neocynipsea (Diptera: Sepsidae). Based on microsatellite genotypes, we first inferred a baseline demographic history using Approximate Bayesian Computation. We then used genomic data from pooled DNA of natural and laboratory populations to test for past interspecific gene flow based on allelic configurations discordant with the inferred population tree (ABBA–BABA test with D-statistic). Comparing the detected signals of gene flow with the contemporary geographic relationship among interspecific pairs of populations (sympatric vs. allopatric), we made two contrasting observations. At one site in the French Cevennes, we detected an excess of past interspecific gene flow, while at two sites in Switzerland we observed lower signals of past microsatellite genotypes gene flow among populations in sympatry compared to allopatric populations. These results suggest that the species boundaries between these two species depend on the past and/or present eco-geographic context in Europe, which indicates that there is no uniform link between contemporary geographic proximity and past interspecific gene flow in natural populations.
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