Morphometric and meristic diversity of the species Scolopendra cingulata Latreille, 1829 (Chilopoda: Scolopendridae) in the Mediterranean region

Abstract

Scolopendra cingulata Latreille, 1829 is the commonest scolopendromorph species in the Mediterranean area. However, its morphological and geographic variation has not been examined so far, and therefore robust hypotheses about the factors that have shaped that variability are lacking. We examined, using multivariate methods for 19 morphometric and meristic characters, the morphological variation of that species using a comprehensive sample of 503 adult specimens from 130 restricted geographic localities. The localities were distributed in three major geographic areas (Balkans, Asia Minor-Middle East, and Italy) in order to discern biological entities and to estimate the morphological relationships between populations and geographic regions. Results showed significant differences between the three geographic groups. Characters such as the distance between the paramedian sulci of the 7th and 8th tergite, the number of antennal segments, the number of spines on the dorsal side of 21st prefemur and number of spines on the 21st prefemoral process significantly discriminated populations of S. cingulata along a west–east geographic gradient. Both eastern (Balkan) and easternmost populations (Asia Minor-Middle East) showed higher mean values of antennal articles and spines of 21st prefemur than the Italian populations. No significant morphological variation was discovered between the sexes of S. cingulata apart from cephalic width and distance between the two paramedian sulci of the 7th and 8th tergite. Based on certain morphometric differences among the three major geographic regions, we suggest that S. cingulata originated in the east and colonized south European area from two different geographic routes. It is suggested that west–east morphological trend of S. cingulata is related either to the prominent palaeogeographic events of the area or to the competition with S. oraniensis Lucas, 1846 in the western Mediterranean.

Introduction

Morphological variation is often attributed to differential adaptations to diverse habitats. Therefore, the study of intraspecific morphological variation is a necessary tool to understand the diversity of life, and to examine if morphological variability can be attributed to selection by ecological and environmental factors or is the result of palaeogeographic history (Adams et al., 2004, Kamilari and Sfenthourakis, 2009).

The evolution of a dynamic geological system such as that of the Mediterranean region has affected the distribution of many terrestrial animals. Mediterranean is characterized by numerous and occasionally complex geographic events in the past (Roegl and Steininger, 1983) (Fig. 1). Therefore, in modern phylogeographic studies, the Mediterranean represents a model area from which to infer intra- and interpopulation variation among geographically distinct areas, such as the Balkan, Anatolian, Middle Eastern and Italian peninsulas. In particular, spatially and temporally fragmented habitats (e.g. islands, mountainous peaks) are used to understand evolutionary processes that might provide answers on species and/or population variability. There are numerous works using molecular data in conjunction with the palaeogeography of the Mediterranean area to study population differentiation among land snails (Douris et al., 1995, Parmakelis, 2003), scorpions (Parmakelis et al., 2006) and vertebrates (Poulakakis et al., 2003, Kasapidis et al., 2005, Kornilios et al., 2005, Poulakakis et al., 2005, Thanou et al., 2005, Tryfonopoulos et al., 2008). However, morphological phylogeographic studies are few although multivariate morphometric analysis has been shown to demonstrate complex, multidimensional patterns of variation and has been proved to be a powerful and reliable method for analyzing intraspecific relations. There are few such works, dealing with beetles (Chatzimanolis et al., 2003), butterflies (Dennis et al., 2000), snails (Giokas, 2000) and vertebrates (Tsekoura et al., 2002, Fraguedakis-Tsolis et al., 2009).

Based on the Chilobase (an electronic database, publicly and freely available through the World Wide Web – http://chilobase.bio.unipd.it/, last updated 2006), the order Chilopoda comprises around 3500 valid species out of an estimated global fauna of approximately 8000 species (Adis and Harvey, 2000). There are nearly 700 species of scolopendromorph centipedes worldwide (Chilobase, 2006). The Scolopendridae is one of the largest families in the Order Scolopendromorpha, including approximately 10% of the world's centipede diversity (Menon et al., 2003). The family has been the subject of research around the world (for example Schileyko and Minelli, 1998, Shelley and Kiser, 2000, Chagas-Jr, 2001, Shelley, 2002, Shelley, 2006, Shelley et al., 2005). The commonest genus within the family Scolopendridae (Newport, 1894) is the genus Scolopendra (Linnaeus, 1758). Species of Scolopendra Linnaeus, 1758 are widespread in all tropical, subtropical and warm temperate areas (Lewis, 1981). Until recently, the taxonomy of Scolopendra was based exclusively on external morphology. Würmli, 1978, Würmli, 1980 produced a comprehensive taxonomic revision of Scolopendra species (canidens group), examining thousands of specimens and identifying, for the first time, 21 qualitative and quantitative morphological characters. However, more recent studies have concentrated on the systematics and distribution of certain Scolopendra species (Shelley, 2002, Shelley, 2006, Shelley et al., 2005). Simaiakis and Mylonas (2008) have shown that there are nine species distributed in the Mediterranean region. Among them Scolopendra cingulata (Latreille, 1829) is the most widely distributed species, and it also occurs in western Asia.

The main aim of this work was the investigation and explanation of the patterns of morphological variation of S. cingulata in the southern Mediterranean region, in relation to the geography and palaeogeography of that area. We used sample material collected from sites that provide comprehensive coverage of the main distributional range of S. cingulata in the Mediterranean. We examined these samples using, for first time in that species, multivariate analyses for a series of established and new quantitative morphological characters (morphometric and meristic). We sought to improve the statistical accuracy and reliability and also to identify the major morphological characteristics that differentiate geographic groups within that species, and to look for possible morphological adaptations related to the diversification processes in this taxon.