Freshwater unionid mussels threatened by predation of Round Goby (Neogobius melanostomus).

Indigenous freshwater mussels (Unionidae) are integral to riverine ecosystems, playing a pivotal role in aquatic food webs and providing ecological services. With populations on the decline worldwide, freshwater mussels are of conservation concern. In this study, we explore the propensity of the invasive Round Goby (Neogobius melanostomus) fish to prey upon indigenous freshwater mussels. First, we conducted lab experiments where Round Gobies were given the opportunity to feed on juvenile unionid mussels and macroinvertebrates, revealing rates and preferences of consumption. Several Round Gobies consumed whole freshwater mussels during these experiments, as confirmed by mussel counts and x-ray images of the fishes. Next, we investigated Round Gobies collected from stream habitats of the French Creek watershed, which is renowned for its unique and rich aquatic biodiversity. We developed a novel DNA metabarcoding method to identify the specific species of mussels consumed by Round Goby and provide a new database of DNA gene sequences for 25 indigenous unionid mussel species. Several of the fishes sampled had consumed indigenous mussels, including the Elktoe (non-endangered), Creeper (non-endangered), Long Solid (state endangered), and Rayed Bean (federally endangered) species. The invasive Round Goby poses a growing threat to unionid mussels, including species of conservation concern. The introduction of the invasive Round Goby to freshwaters of North America is shaping ecosystem transitions within the aquatic critical zone having widespread implications for conservation and management.

Redescription of Pseudotropheus livingstonii and Pseudotropheus elegans from Lake Malawi, Africa.

Pseudotropheus livingstonii and P. elegans are two sand-dwelling cichlid species that belong to the so-called mbuna, a group of predominantly rock-dwelling haplochromines of Lake Malawi. The identity of these two species has confused taxonomists for almost a century until a recent rediscovery of representatives of P. elegans close to its type locality. New diagnoses for both species are provided.

Schistosoma haematobium in Lake Malawi: susceptibility and molecular diversity of the snail hosts Bulinus globosus and B. nyassanus.

Intermediate hosts of Schistosoma haematobium, the causative agent of urinary schistosomiasis, in Lake Malawi include: Bulinus globosus, a member of the B. africanus group and B. nyassanus, a diploid member of the B. truncatus/tropicus species complex. We compared genetic variability between isolates of S. haematobium from the southern part of the lake (Cape Maclear), where both B. globosus and B. nyassanus play a role as intermediate hosts, and isolates from the northern part, where only B. globosus is host. Data show that the S. haematobium isolates from these two areas of Lake Malawi cannot be distinguished using nuclear or mitochondrial sequences and are capable of cross-infections.

The schistosome intermediate host, Bulinus nyassanus, is a 'preferred' food for the cichlid fish, Trematocranus placodon, at Cape Maclear, Lake Malawi.

Over the last decade, transmission of the schistosome parasites of humans has increased in parts of Lake Malawi, possibly because over-fishing has led to a decline in the numbers of molluscivorous fish. The stomach contents of 51 wild-caught Trematocranus placodon from the Cape Maclear area of Lake Malawi have now been investigated and compared with the field abundance of snail species at two sites, close to where the fish were caught. The snails found in the fish stomachs were identified to genus or species on the basis of their shell fragments and/or opercula. The sizes of the prosobranchs consumed by the T. placodon were determined from their operculum sizes whereas the Bulinus nyassanus ingested by the fish were categorized as small (<4 mm) or large (> or =4 mm) on the basis of their shell fragments. The proportion of the Bu. nyassanus ingested that were categorized as large increased with fish size. Furthermore, the relative abundance of Bu. nyassanus in the guts of the fish was considerably higher than in the field, indicating that the T. placodon had a 'preference' for Bu. nyassanus over the Melanoides species that dominated the snail fauna. Small specimens of Bellamya species were also consumed in a greater proportion than found in field.

Evolution of NADH dehydrogenase subunit 2 in east African cichlid fish.

The complete sequence (1047 bp) of the mitochondrially encoded ND2 gene was obtained from 31 species of cichlid fishes to investigate the evolutionary history of the species flocks of the East African lakes. The observed pattern of nucleotide substitution in this sequence is typical of mitochondrial genes, showing a high transition bias and rapid mutational saturation, especially at codon positions where base frequencies are unequal. The base composition of the third position of codons is heterogeneous among species, suggesting frequent shifts in the pattern of substitution. Phylogenetic analysis of the sequences shows that the mtDNA variation in Lake Malawi cichlids is nested monophyletically within the range of variation shown by Tanganyikan cichlids. The closest Tanganyikan relatives of the Malawi flock are members of the tribe Tropheini. Classifications based on morphology are generally supported by the mtDNA data, with some significant exceptions in the Tropheini and Lamprologini. Because of an apparently rapid radiation of the Tanganyikan lineages, it is difficult to assess the basal topology of the Tanganyikan radiation at this time. Divergences among tribes are consistent with an intralacustrine radiation within the past 10 million years.

Intra- and interspecific mitochondrial DNA sequence variation within two species of rock-dwelling cichlids (Teleostei: Cichlidae) from Lake Malawi, Africa.

Difficulties in interpreting the evolutionary significance of Lake Malawi cichlid morphologies led us to examine molecular techniques for resolving relationships among closely related species. Mitochondrial DNA (mtDNA) sequence variation in the first half of the control region (445 bp) was examined within and between two species of Melanochromis, a genus of rock-dwelling cichlids from Lake Malawi, Africa. The mean number of pairwise differences observed within Melanochromis auratus (Boulenger) and Melanochromis heterochromis Bowers and Stauffer mtDNA haplotypes was 2.0 (0.45%) and 5.0 (1.13%), respectively, and a mean of 4.9 (1.11%) pairwise differences between the two species was observed. Mean pairwise differences between Melanochromis species and Pseudotropheus zebra (Boulenger), another species of rock-dwelling cichlid and Tramitichromis cf. liturus, a sand-dwelling genus, were 11.2 (2.52%) and 21.9 (4.93%), respectively. Species divergence and radiation within the genus Melanochromis appears to have occurred rapidly and recently. Mitochondrial DNA sequence variation within this genus was sufficient for generating hypotheses concerning the evolutionary relationships within the genus and for examining generic-level relationships within and among the major cichlid lineages in Lake Malawi.

Similar morphologies of cichlid fish in Lakes Tanganyika and Malawi are due to convergence.

The species flocks of cichlid fishes in the lakes of East Africa are the most spectacular example of adaptive radiation among living vertebrates. Similar highly derived morphologies are found among species in different lakes. These similarities have been variously interpreted either as evidence for migration of ancestral species between the lakes, or of striking convergence of morphology. To distinguish among these competing hypotheses we sequenced a portion of the mitochondrial DNA control region from six pairs of morphologically similar taxa from Lakes Malawi and Tanganyika. Our results clearly indicate a separate origin of these morphologies in the two lakes. They also suggest that the Tanganyikan radiation is relatively old, and that the species flocks in lakes Malawi and Victoria are derived from one of the ancient lineages found in Lake Tanganyika. These findings have important implications for understanding the pattern of morphological and behavioral evolution in these fish.

Fish predation as a factor in the distribution of Lake Malawi gastropods.

Gastropod densities in Lake Malawi, Africa drop dramatically below 4.5 m water depth. Weed beds disappear and the number of molluscivorous cichlids increases below this depth. When molluscivores were excluded from open sand habitat by cages, due to migration and reduced predation, the density of snails increased by 40-60% within a week. Alternatively, when adult Cyrtocara placodon were placed into the cages, snail density equaled the controls. The molluscivores disproportionately consumed snails of the genus Bulinus relative to those of the more heavily armoured genus, Melanoides. Cichlid molluscivores are hypothesized to be responsible for preventing the thin shelled bilharzia vector snail, Bulinus globosus, from successfully invading the open shore areas of Lake Malawi. Lake Malawi may be relatively free of this human disease because of snail predation by cichlids.

Temperature preference of the crayfish Orconectes obscurus.

Acclimation temperature influenced the acute preferred temperature of the crayfish Orconectes obscurus. This species preferred a higher temperature than its acclimation temperature for those acclimation temperatures ranging from 6 degrees to 26 degrees C. When acclimated to 30 degrees and 33 degrees C, the crayfish preferred a lower temperature than its acclimation temperature. The final temperature preferendum is estimated to be approximately 30 degrees C.