Evolution of the mitochondrial DNA control region in the mbuna (Cichlidae) species flock of lake Malawi, East Africa

Considerable controversy has surrounded the application of mitochondrial DNA data to reconstruction of evolutionary relationships among the endemic cichlids of Lake Malawi. Central to this debate has been the issue of whether lineage sorting is complete, and thus whether these data actually reflect species phylogeny, or simply gene genealogy. Review of all mtDNA control region sequences available for members of one monophyletic subset of this species flock, the Malawi rockfishes, or mbuna, strongly indicates that lineage sorting is incomplete: Character-based analyses of these sequences reconstruct gene, not species, interrelationships. Analysis of the pattern of nucleotide substitutions differentiating these mtDNA alleles suggests that pyrimidine residues undergo transition substitutions more often than do purines. Estimation of the magnitude of derived sequence differentiation in light of the reconstructed gene genealogy suggests that the mbuna may be of considerably more recent vintage than previous molecular characterizations have indicated. Received: 6 April 1996 / Accepted: 3 March 1997     

Inheritance of allozymes in Atlantic herring (Clupea harengus harengus)

Progeny from single pair crosses of Atlantic herring were examined to determine the heritability of genetic variation at seven polymorphic allozyme loci. Mendelian inheritance of codominant autosomal alleles was established for IDH-2, LDH-1, LDH-2, ME-2, PGM-1, and PGI-2. This demonstration of Mendelian inheritance is essential for accurate interpretation of allozymic variation among natural populations of this pelagic species.     

Origin, diversification, and historical biogeography of the genus Trachurus (Perciformes: Carangidae)

We addressed phylogenetic relationships in the genus Trachurus using cytochrome b gene and D-loop sequences. The trees showed five groups: (1) the Southwest Pacific species (T. japonicus, T. novaezelandiae, and T. declivis); (2) The Mediterranean Sea and Eastern Atlantic species (T. mediterraneus); (3) The Atlantic Ocean species (T. lathami and T. trecae); (4) Eastern Atlantic species (T. trachurus and T. capensis); and (5) a group of highly mobile pelagic species, two from the Eastern Pacific (T. symmetricus and T. murphyi) and one from the Eastern Atlantic (T. picturatus). The phylogeny based on Cyt b, supports the molecular clock hypothesis and our results agree with the reported fossil indicating that the origin of this genus occur when the Thetys Sea closed (around 18.4 MYA). In addition, a very slow neutral substitution rate is reported identified only two periods of maximum diversification: the first occurring between 18.4 and 15.0 MYA and the second between 8.4 MYA and present day.     

Resolution of the taxonomic status of Chilean and Californian jack mackerels using mitochondrial DNA sequence

Phylogeographic reconstructions using mitochondrial DNA sequences from both the control region and the cytochrome b gene demonstrated that two disjunct populations be recognized as Trachurus murphyi and Trachurus symmetricus. The species have been isolated for at least 250 000 years.     

Polygynandry inPseudotropheus zebra, a cichlid fish from Lake Malawi

Synopsis Parental care in the Malawian cichlid fishPseudotropheus zebra BB is extensive and exclusively maternal; males contribute only genetic material. The costs of searching for multiple mates (in this case risk of predation on orally incubated eggs) suggested that females should be monandrous; microsatellite genetypes of seven brooding females and their young, however, reveal extensive multiple paternity in this species, with a mean of 3.8 paternal individuals per brood. Polygynandry inP. zebra is probably not maintained by selection for genetically diverse offspring; potential explanations include avoidance of inbreeding, and bet-hedging on other male characteristics that females are unable to evaluate when selecting a mate. The observed degree of multiple paternity strongly suggests that females are free to choose mates as they will, a prerequisite of many theories positing sexual selection as a key element in Malawi chichlid evolution. It should also result in elevation of effective population sizes, and thus be antagonistic to runaway evolution of male secondary sexual characteristics, but not necessarily to other modes of sexual selection.     

Reduced Genetic Diversity and Effective Population Size in an Endangered Atlantic Salmon (Salmo Salar) Population from Maine, USA

Atlantic salmon (Salmo salar) populations in Maine, USA, are listed as a Distinct Population Segment under the U.S. Endangered Species Act due to reduced spawning runs and juvenile densities. Whenever possible, optimal conservation strategies for endangered populations should incorporate both present and historical knowledge of genetic variation. We assayed genetic diversity at seven microsatellite loci and at the mitochondrial ND1 gene in an endangered wild population of Atlantic salmon captured from the Dennys River from 1963 to 2001 using DNA’s extracted from archival scale and tissue samples. We examined temporal trends of genetic diversity, population structure, and effective population size (Ne). Overall temporal trends of diversity and Ne show significant reductions from 1963 to 2001 raising the possibility that current restoration efforts may be impacted by historical loss of diversity potentially critical to adaptation. Although our results suggest genetic stability in this population from 1963 to 1981, significant differentiation was observed for both the 1995 and 2001 samples compared with all other temporal samples. The presence of an ND1 mtDNA haplotype in this population, historically observed only in European and Newfoundland stocks, may represent previously unrecognized local wild diversity or, alternatively, may represent introgression from non-native fish.     

Molecular insights into Cumacean family relationships (Crustacea, Cumacea)

Cumaceans are a diverse order of small, benthic marine crustaceans. Phylogenetic hypotheses for the eight currently recognized cumacean families have not been formally proposed. However, based on external morphological traits and Linnean classification, a few conflicting hypotheses of relatedness have been proposed. Family definitions rely on morphological characters that often overlap and diagnoses are based on a combination of non-unique characters. Morphological analysis does not provide a well-resolved phylogeny. In the present study, we use amino acid sequences from the mitochondrial cytochrome oxidase I gene to produce a molecular phylogenetic hypothesis for the families of Cumacea. Phylogenetic analyses at the amino acid level were performed under Bayesian, likelihood, and parsimony methods. Results strongly suggest that families lacking an articulated telson form a monophyletic group. This pleotelson clade, composed of the families Bodotriidae, Leuconidae, and Nannastacidae, is the most derived within the Cumacea. Within this group, the Bodotriidae resolve paraphyletically, with Leuconidae and Nannastacidae embedded within it. Comparison of the molecular phylogeny with that based on morphology suggests that many "diagnostic" characters are homoplasious.