Villegasia, 1966
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publication ID |
https://doi.org/ 10.1007/s13127-015-0203-0 |
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persistent identifier |
https://treatment.plazi.org/id/03E387E7-FFB8-794B-FCDA-FC111848695B |
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treatment provided by |
Felipe |
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scientific name |
Villegasia |
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Genus Villegasia
Dodge (1966) erected the genus Villegasia , which originally included two species: Sarcophaga postuncinata Hall, 1933 and Villegasia difficilis Dodge, 1966 , the latter designated as type species. Subsequently, Tibana and Lopes (1985) described Villegasia pernambucana and in the same publication these authors considered V. difficilis as a synonym of S. postuncinata , and they also transferred Sarcophaga almeidai Lopes, 1938 to Villegasia . Currently, the classification proposed by Tibana and Lopes (1985) is still in use. In the present study, we included all species of Villegasia and we found this genus to be monophyletic, supported by three uniquely derived apomorphies: (1) sternite V blackish, (2) syntergosternite 7+8 entirely black, and (3) distal margin of the juxta with spines. The first and second apomorphies correspond to coloration features that may be variable even between individuals of the same species, which makes its phylogenetic signal unreliable.
Two character states were shared between Villegasia and the subgenus Squamatodes : (1) cercal prong with dorsal surface angulated, and (2) vesica reduced. Species of these groups, possess only one opening in the acrophallus, however each opening has an independent origin. Squamatodes species do not possess capitis or median process, and the only acrophallic opening is a result of a fusion of the lateral styli (Fig. 3d). Some differences were identified in the acrophallic structures of Villegasia with regard to those of Squamatodes . Species of Villegasia posess lateral styli collapsed, and their unique opening of the acrophallus is here interpreted as the opening of the median process (Fig. 1d, e).
Informative power of characters and evolution of male genitalia
External features are very homogeneous across the genera in the subfamily Sarcophaginae , while the male terminalia features are highly complex ( Aldrich 1916; Roback 1954; Pape 1987; Dahlem and Downes 1996; Giroux et al. 2010) and thus provide more informative characters ( Giroux and Wheeler 2009; Giroux et al. 2010; Whitmore et al. 2013). Male terminalia have been widely used for species recognition and have provided most of the phylogenetic information in the cladistic analysis of the Peckia clade. This was consistent with other studies in the Sarcophagidae family ( Blackith et al. 1997) and with other insect groups ( Song and Bucheli 2009).
Most of the clades at the generic and subgeneric levels of our morphology-based trees were supported only by characters of the terminalia, which confirms that male genitalic characters are informative in resolving phylogenetic relationships at various levels ( Song and Bucheli 2009). Structures of male genitalia are useful in systematics due to their composite nature, which probably reflects that all parts are functionally different from each other ( Song and Bucheli 2009). For instance, the folded phallotreme, supports the monophyly of the subfamily Sarcophaginae , while its parts support clades at lower hierarchical levels. Thus, the reduction of the median process supported the clade (( Helicobia + Sarcophaga ) + Lipoptilocnema ) + Peckia )), while the elongation of the capitis supported (( Helicobia + Sarcophaga ) + Lipoptilocnema ), and the expansion of the base of the lateral styli supported Engelimyia . Similar findings of male genitalic characters that support phylogenies at various levels have been observed in other groups of insects, such as the muscid tribe Coenosiini ( Couri and Pont 2000) , Tabanomorpha ( Zloty et al. 2005), in the planthoppers ( Hemiptera : Cixiidae ) ( Hoch 2006), and in microgastrine braconid wasps ( Whitfield et al. 2002).
In general, molecular-based trees were more resolved than those based on morphological characters, although both showed polytomies. Differences in resolution might be explained by differences in size of matrices (3458 molecular characters versus 115–116 morphological characters). However, it is noticeable how the morphology-based trees were able to recover generic and subgeneric clades consistently. Here, it is possible to suppose that in morphology-based trees, different parts of the terminalia generate support for different hierarchical levels due to their different rates of evolution, being able to recover the relationships of a large taxa sampling of different genera, subgenera and species with a relatively small number of characters. In addition, when comparing shallow-level relationships in molecular- and morphology-based trees, the sequence divergence shown by short branches between species that possess distinctive male genitalic set of characters, may indicate a rapid rate of morphological divergence compared to that of molecular sequences. For instance, sequence divergence between P. (Pattonella) intermutans and P. (Squamatodes) ingens is low, which is inferred by the short branch length between them ( Fig. 9 View Fig ), but these species have the male genitalia dramatically different ( Fig. 5a, b View Fig ), which allows us to speculate that the shallow-level rate of evolution in male genitalia is higher compared to that of molecular characters. Studies have shown that evolution of the structures that compose the male genitalia is particularly rapid in those characters under pressures of sexual selection ( Eberhard 1985; Hosken and Stockley 2004; Jensen et al. 2009), which are those characters of species which mate multiple times and those where a direct contact between male and female genitalic structures occur. Species of the genus Peckia fulfil both criteria, which makes this genus and other sarcophagids as good models to understand how sexual selection operates on the evolution of the genitalia. At this date, there is no solid knowledge on the function of each genital structure in sarcophagids. There are no available studies that explain how the different sections of the acrophallus (i.e., median process, capitis and lateral styli) and other phallic structures like the harpes, juxta, paraphallic lateral plates, and vesica interplay with the female genitalia. There is, however, some information available about how in the mating the female genitalia have physical contact to other non-phallic structures of the male terminalia such as the pregonites, sternite V, and the cerci, with the latter serving an important role during copulation. Lopes and Kano (1968) showed that in Peckia (Peckia) chrysostoma (Wiedemann, 1830) [= Paraphrissopoda chrysostoma ], the phallus together with the cercal prongs are inserted into the oviduct. Although it is difficult to identify the exact function of each structure of the terminalia, we can speculate on the shape and spine pattern of the cerci. In subgenera of Peckia the posterior face of the cerci is very variable, showing minute spines and swollen sections in species of Euboettcheria , saddle-shaped concavities followed by a medial tooth-like projection in species of Peckia (s. str.) or posterior surface abruptly bent in Pattonella or slightly angulated in Squamatodes . Cerci in species of subgenus Euboettcheria are species-specific, and may be useful for identification of closely related species that otherwise possess near-identical phallic structures (see Buenaventura and Pape 2013: figs. 22, 23, 25–31, 33–38, 40–42, 44–52). Thus, the ornamentation of cercal prongs when entering into contact with the wall of the oviduct could stimulate the female during copulation or serve as sensory structures, since they are covered with minute setae and spines, and the morphological variability could be driven by female choice. Thus, it might be a rapid divergence in the shape of the male genitalic structures like the cerci, as predicted by sexual selection theory by cryptic female choice hypothesis ( Eberhard 1985; Arnqvist and Danielsson 1999; Hosken and Stockley 2004), and the shape of the cerci might include candidate characters as internal courtship devices to be affected by the female choice. Other male genitalic organs that may be candidates are the pregonites, mainly because they show high variation at both subgeneric- and species-level in species of Peckia ( Buenaventura and Pape 2013) , and also because their character states support species-level relationships within Euboettcheria in our phylogeny, and they are in physical contact with the female genitalia by pressing the vaginal plates during copulation ( Lopes and Kano 1968). Although there is no obvious relation between the morphological variation of cerci and pregonites and the sperm transfer, the role of these organs are likely to be correlated with reproductive success.
The number of male external characters was lower than those of the male terminalia, however, they provided support for clades at generic and subgeneric levels. For instance, one third of the characters supporting the monophyly of the genus Helicobia corresponded to external characters, while at least one character state that supported the monophyly of Engelimyia and Peckiamyia was from body parts different from the male terminalia. At lower taxonomic level, monophyly of subgenus Pattonella and its sister-relationship to Squamatodes was based on external characters from the prosternum, hind coxa, postalar wall, and abdominal sternites. Interestingly, the single character of female genitalia included in our matrix came out as informative for the monophyly of the genus Helicobia . On the other hand, none of the two larval characters was informative in our analyses, which was probably due to the scarce available data for the species studied.
We observed that morphological data under the first and second character-coding schemes on their own provide weak support for, or fail to resolve, some deep nodes; and molecular data on their own yield trees that contain implausible and weakly supported clades. However, currently, there is no clarity on the morphological definition of many genera of Sarcophaginae , where the mostly phenetic diagnoses ( Pape 1996) have not yet been phylogenetically tested. In this context, unexpected associations between some groups that have never been studied in a phylogenetic context do not contradict any hypothesis but instead build on the knowledge of the systematics of Sarcophaginae .
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