Peckia, Robineau-Desvoidy, 1830

Buenaventura, Eliana & Pape, Thomas, 2015, Phylogeny of the Peckia-genus group: evolution of male genitalia in the major necrophagous guild of Neotropical flesh flies (Diptera: Sarcophagidae), Organisms Diversity & Evolution (New York, N. Y.) 15 (2), pp. 301-331 : 302-303

Peckia and the Peckia clade

Robineau-Desvoidy’ s (1830) original concept of Peckia included 17 nominal species, most of which are now scattered in various other genera. In his pioneering work on Neotropical flesh flies, Lopes (1941, 1943, 1958) provided a first attempt at circumscribing Peckia and B related genera^. Roback (1954) was the first to conduct a thorough comparative study of flesh fly male terminalia, proposing a series of characters that were considered of phylogenetic (or in pre-Hennigian terminology B evolutionary^) importance, and he included the species here considered under Peckia in his subtribe Sarcodexiina . Lopes (1969) proposed a classification of subfamily Sarcophaginae with six tribes, indicating that further tribes would soon be added. In a subsequent study of the first instar larva ( Lopes 1983), his classification was augmented with five tribes. One of these tribes was Sarcodexiini, which apart from Peckia [in the wide sense of Pape (1996)] included the genera Argoravinia Townsend , Helicobia Coquillett , Lipoptilocnema Townsend , Sarcodexia Townsend , Torgopampa Lopes , and Villegasia Dodge.

Pape and Mello-Patiu (2006), in their revisionary work on Engelimyia Lopes , suggested that Engelimyia together with Malacophagomyia Lopes , Peckia , Peckiamyia Dodge , Sarcodexia , and Titanogrypa Townsend may form a monophylum based on the absence of presutural dorsocentral setae. Also, they argued against Lopes’ (1975, 1983) inclusion of Engelimyia as part of Paraphrissopoda Townsend (synonymised under Peckia by Pape (1996)), based on morphological characters of both larvae and adults. Giroux et al. (2010), in their morphology-based analysis, defined the B Peckia clade^ to include the genera Engelimyia , Peckia , Sarcodexia , and Titanogrypa . It should be noted that Malacophagomyia and Peckiamyia were not included in their analysis. Giroux et al. (2010) specifically found the topology ( Engelimyia ( Peckia ( Sarcodexia + Titanogrypa ))). However, only one or a few species of each genus were included. Recent phylogenetic analyses based on molecular data have been presented by Kutty et al. (2010) and Stamper et al. (2012), but with limited—and very different—taxon sampling. Kutty et al. (2010) had Sarcodexia + Villegasia as the sister group of a paraphyletic Peckia (containing Peckiamyia ), and the sister clade of this group was composed of species of Sarcophaga Meigen. Both Engelimyia and Titanogrypa were included but they did not group with the other members of the Peckia clade. Stamper et al. (2012) had a moderately supported sister-group relationship between Peckia and Sarcophaga , and Helicobia emerged as the sister group of these two genera but with no branch support. Titanogrypa formed a paraphyletic assemblage at the base of subfamily Sarcophaginae .

Most recently, Piwczyński et al. (2014) analyzed the combined molecular data available for Sarcophagidae on GenBank. Their favored tree shows a clade of Peckia (including both Sarcodexia and Villegasia ) + Sarcophaga , with Engelimyia , Helicobia , Peckiamyia , and Titanogrypa scattered on the remaining tree. However, support values are generally too low to make any firm conclusions on the phylogeny of the Peckia clade.

We consider the Peckia clade as containing the genera Engelimyia , Helicobia , Lipoptilocnema [included as a subgenus within Sarcophaga by Pape (1996)], Peckia, Peckimyia , Sarcophaga , Titanogrypa , and Villegasia . The monophyly of this clade needs formal corroboration, and we deliberately abstain from giving this clade a rank within the subfamily classification. The intent is to have a short name for making reference to a set of genera that may form a monophylum, and as such provide an ideal setting for a phylogenetic analysis of Peckia . This taxon coverage also facilitates the proposal of precise, detailed, and stable phylogenetic homologies ( Nixon and Carpenter 2012) among taxa whose phylogenetic position has questioned the monophyly of the genus Peckia (sensu Buenaventura and Pape 2013) . In recent molecular- and morphology-based phylogenetic analyses, this genus emerged as paraphyletic with regard to Titanogrypa ( Giroux et al. 2010) , Villegasia ( Kutty et al. 2010; Piwczyński et al. 2014), and Peckiamyia ( Kutty et al. 2010) . The most probable sister-group of Peckia is still ambiguous and with some very different, competing hypotheses ( Giroux et al. 2010; Kutty et al. 2010; Stamper et al. 2012; Piwczyński et al. 2014). The increased taxon sampling compared to previous studies ( Giroux et al. 2010; Kutty et al. 2010; Stamper et al. 2012; Piwczyński et al. 2014) is expected to provide critical information needed to assess synapomorphic features and character state transformations of the ingroup taxa.

Phylogenetic homology and explanatory power

Characters of the male terminalia in Sarcophagidae are known for their utility in species identification (e.g., Pape and Mello-Patiu 2006; Giroux and Wheeler 2009; Mulieri and Mariluis 2011; Vairo et al. 2011; Buenaventura and Pape 2013). In the flesh fly subfamily Sarcophaginae , the intricate male terminalia appear to be particularly informative for morphology-based phylogeny reconstruction ( Roback 1954; Sugiyama and Kano 1984; Pape 1994, 1998; Blackith et al. 1997; Giroux et al. 2010; Whitmore et al. 2013). The high complexity in the male genitalic structures and the continued discovery of new morphological variation and undescribed structures in species of the Peckia clade require a revision of the existing phylogenetic homology hypotheses for some structures that are usually considered of high diagnostic value. In particular, the median stylus has been shown to vary across genera of Sarcophaginae (e.g., Giroux et al. 2010), although to a lesser degree at the species level (e.g., Whitmore et al. 2013; Giroux et al. 2010). However, with an increasingly finegrained homology assessment of the structural complexities, the hypotheses of phylogenetic homology will have more explanatory power but also be progressively more prone to falsification ( Grant 2002). In addition, morphological characters are subject to homoplasy due to either evolutionary convergence (e.g., Scotland et al. 2003; Springer et al. 2007), or due to character misclassification stemming from observer error ( Givnish and Sytsma 1997). For these reasons, they have been considered as problematic ( Scotland et al. 2003; Eick et al. 2005) and less desirable ( Hedges and Maxson 1996) for phylogenetic analyses. A plausible solution for homoplasic morphological traits is to first objectively identify if the phylogeny is affected by convergence either by using a qualitative strategy (see the set of criteria by Wiens et al. 2003) or a statistical approach ( Holland et al. 2010); and next to exclude the characters found to be homoplasic. Much more can be done to address problems of structural complexity and homoplasy due to character misclassification when a precise definition of characters (i.e., hypotheses of homology) provides a possible solution. A more accurate hypothesis of phylogenetic homology, which explains more of the morphological variation, can be reached by coding such morphological complexes with an atomization approach ( Bruneau 1997). An atomized coding, detailing specific morphological aspects of the male terminalia, should increase the phylogenetic signal and highlight differences in otherwise apparently convergent morphologies. The sole consideration of a single presence/absence character may require an ad hoc hypothesis of homoplasy, while atomizing the complex into several characters may remove the conflict and increase the consistency.

The purpose of the present paper is to examine structures and observe similarities of the male terminalia within the Peckia clade in order to hypothesize phylogenetic homologies by using an atomization approach for coding characters, and compare different codifications through congruence between characters. At the same time, we aim at providing an extensive, parsimony-based phylogenetic analysis of the Peckia clade with particular focus on the genus Peckia , including a comparison of the phylogenetic signal in available morphological and molecular datasets.