Patterns of evolutionary tempo and mode in the radiation ofMelanopsis(Gastropoda; Melanopsidae)

Abstract

The Paratethyan basins of eastern Europe and western Asia became isolated from marine influence in the Late Miocene, and were the sites of several remarkable endemic radiations of brackish and freshwater organisms. Here I describe the patterns of tempo and mode before and during the radiation of the gastropod Melanopsis in the Pannonian basin of eastern and central Europe, and I explore the underlying mechanisms of evolutionary change.The most ancient melanopsid species in this area, M. impressa, was present in freshwater areas marginal to the basin well before the radiation. Widely spaced samples of M. impressa indicate that this species underwent a period of stasis lasting at least 7 m.y. The end of stasis corresponded with the extinction of the last of the normal marine fauna in the basin, suggesting that the lack of other fauna and/or reduced salinity in the basin permitted expansion of the melanopsids from the basin margins into the basin proper. Stasis ended with the onset of changes in size, shouldering, and ontogeny, which led eventually to M. fossilis. Change occurred over a 2-m.y. interval; a series of intermediates is present for all three characters. Within-sample correlations provide no evidence that the three characters are constructionally linked; instead they appear to be changing independently. The mode of change in the M. impressa–M. fossilis lineage appears to have been anagenetic. Alterations in the rate and direction of selection (and/or genetic links between characters) are probably required to explain the overall slowness of the change.Most Pannonian basin melanopsid species arose by rapid cladogenesis in the Middle Pannonian Stage. Physical factors in the basin probably influenced the timing of this diversification; contrasting patterns of variation and diversity between two melanopsid clades suggest that intrinsic factors influenced the extent of diversification.

A gastropod-based biogeographic scheme for the European Neogene freshwater systems

“…Throughout the Neogene, the family Melanopsidae was very dominant and even increased its number of species over time. Particularly in the long-lived Lake Pannon, Lake Dacia, and the lakes of the Dinaride Lake System it played an important role and formed several independent endemic lineages (e.g., Geary, 1990;Glaubrecht, 1993Glaubrecht, , 1996Bandel, 2000;Geary et al, 2002;Neubauer et al, 2011Neubauer et al, , 2013b. The high relative abundance of up to 16.9% contrasts the present pattern with only 18 species for the whole of Europe (1.7%).…”

Rates of evolution on the time scale of the evolutionary process

“…Separate treatment of rates reported as positive and negative yields an upper median of positive rates of about 0.660 haldanes and a lower median of negative rates of about -0.486 haldanes. Some 50% of all rates are expected to lie outside this range, involving rates on the order of ± 0.5 or more stand- (1948), Haldane (1949), Maglio (1973), McDonald (1981, Malmgren et al (1983), King and Saunders (1984), Flynn (986), Lister (1989), Barnosky (1990), Forsten (1990), Geary (1990), Lich (1990). Gingerich (1991), Heaton (1993.…”

Quantitative Genetics of Bryozoan Phenotypic Evolution. Ii. Analysis of Selection and Random Change in Fossil Species Using Reconstructed Genetic Parameters

“…Patterns of phenotypic evolution based on multiple quantitative morphological characters range from gradual to highly punctuated in welldefined, geographically widespread lineages with detailed fossil records (Cheetham 1986;Wei and Kennett 1988;Geary 1991Geary , 1992Geary , 1993Cheetham and Jackson 1994b). The close correspondence between living, quantitatively discriminated morphospecies and genetic differences validates these patterns as the morphological records of species-level evolution, suitable for evaluating natural selection and random genetic change as the agents ofspeciation (Michaux 1989;Cheetham 1990, 1994;Gould 1991).…”

“…However, the inference of process from pattern is complex and not always intuitive. On geologic time scales, gradual patterns may be too slow to imply prevalence of directional selection (Geary 1991), and punctuated patterns might result entirely from the interaction of stabilizing selection, mutation, and genetic drift, without necessary input from directional selection (Lynch 1990;Cheetham and Jackson 1994b).…”