Species number - body weight distributions are generally thought to be skewed to the right. While this pattern is well documented in vertebrates, comparative studies on species rich invertebrate taxa are still scarce. Here I show that the weight distributions of central European Coleoptera (based on 8257 species body weight data compiled from Freude et al., 1964-1994) are predominantly right skewed. Skewness and species richness per taxon were positively correlated. The number of modes of the body weight distributions was negatively correlated with species richness. 273 of the 558 genera had bimodal distributions. Species richness per genus did not significantly depend on mean genus body weight. In general the coleopteran size distributions differed from those of European Hymenoptera but were similar to the respective distributions of vertebrates. I conclude that we should be cautious when generalizing patterns found in one taxon.
Species of the Agrilus viridis-complex and the genus Trachys are morphologically difficult to identify or even indistinguishable. However, all of them are ecologically clearly separated because their larvae develop in different host plants. Hitherto, it was unclear whether they represent varieties, ecological races or true species. In this paper the genetic variation and phylogenetic relationships within these groups are analysed using partial sequence data from mitochondrial genes (12S rDNA, and a fragment containing regions of ND1 and 16S rDNA). The phylogenetic analyses yielded largely congruent tree topologies and indicate that all species and varieties of the Agrilus viridis-complex belong to a monophyletic group, which is closely related to A. cuprescens. Compared to all other Agrilus-species tested, the genetic distances within the A. viridis-complex are very small. However, all varieties and species are clearly separated. Thus, our data support the view that both the members of the Agrilus viridis-complex and the species of the Trachys-group represent genetically separated taxa.
Colour traits can be elaborated through sexual selection and have potential to drive reproductive isolation. Male three-spined sticklebacks (Gasterosteus aculeatus) express striking visual signals to attract choosy females during courtship, typically expressed as red carotenoid-based pigmentation on their throat and jaw during the breeding season, along with blue eyes and blue/green flanks. The extent and intensity of red colouration in males have been linked to fitness benefits to females, including body condition, parasite resistance, parental ability and nest defence. In some populations in the Pacific Northwest of North America, male three-spined sticklebacks express melanic nuptial colouration. In these populations, male possess black throats instead of red, and have dark or black bodies. Melanic males are associated with waterbodies that are red-shifted due to the presence of tannins, where the ambient light environment is dominated by long wavelengths. Here we report the first discovery outside North America of melanic populations of threespined sticklebacks on the island of North Uist in the Scottish Hebrides, on the northwest Atlantic coast of Europe. These populations are associated with a hotspot of stickleback morphological diversity and occur in association with red-shifted waterbodies.
Polygraphus grandiclava (Thomson, 1886) is a unique scolytid species in that it infests both Pinaceae and Rosaceae. The utilization of such different host trees lead to the designation of two species at the beginning of the last century. Later on, these two species were synonymised. Here we investigated the genetic identity of populations collected from pine and cherry trees by sequencing a partial region of the mitochondrial COI gene. The phylogenetic study presented reveals no indication of host-induced differentiation within the mitochondrial sequences of the populations collected from the two host plants.
The formation of ring species might provide an explanation of how speciation can occur despite ongoing gene flow. However, few species fit all of the criteria of a classic ring species that formed via isolation by distance around a barrier. Population genetic analyses and ecological niche models were used to examine a ring of song sparrow (Melospiza melodia) subspecies that surround the Sierra Nevada in North America. Eight models were compared that included both geography-based and ecology-based scenarios of ring formation. Song sparrows do fit some aspects of a classic ring species that formed via expansion around a barrier; however, admixture rather than complete reproductive isolation occurred when populations met at the terminus of the ring in southern California. Nichemodels show that variation among subspecies is likely to reflect adaptation to local conditions coupled with current limitations to gene flow across ecotones and that birds are likely to have expanded from a refugium in the southwestern United States. Given that simple isolation-based models often fail to explain many ring species patterns, alternative models that incorporate ecological factors might provide a better explanation of how most ring species formed. Isolation and subsequent partitioning of populations by ecotones can be important drivers of geographic variability in ring species.