Phylogenetic relationships and phylogeography of the Killifish species of the subgenus Chromaphyosemion (Radda, 1971) in West Africa, inferred from mitochondrial DNA sequences

Extensive karyotype variability of African fish genus Nothobranchius (Cyprinodontiformes)

Karyotypes of 65 species of the genus Nothobranchius Peters, 1868 were reviewed and of those 35 examined first time. The results of present study have shown that fishes of the genus Nothobranchius possessed highly diverse karyotypes. The diploid chromosome number (2n) ranged from 16 to 50. The most frequent 2n was 2n = 36 (in 35 species) while the second one 2n = 38 (in 13 species). Proportion of biarmed chromosomes varied from 0 to 95% between species. Diploid chromosome number variability apparently exists as a result of chromosomal fusions or fissions and extensive karyotypic formula alterations promoting by inversions. Multiple sex chromosomes of system X₁X₁X₂X₂/X₁X₂Y type were found only in karyotypes of 5 species. The extensive karyotype variability, unusual for teleosts, of genus Nothobranchius can be likely associated with the characteristics of its life cycle and inhabiting under unstable environment of East African savannah temporal pools.

Divergent karyotypes of the annual killifish genus Nothobranchius (Cyprinodontiformes, Nothobranchiidae)

Karyotypes of two species of the African annual killifish genus Nothobranchius Peters, 1868, Nothobranchius brieni Poll, 1938 and Nothobranchius sp. from Kasenga (D.R. Congo) are described. Both species displayed diploid chromosome number 2n = 49/50 for males and females respectively with multiple-sex chromosome system type X₁X₂Y/X₁X₁X₂X₂. The karyotypes of studied species are considerably different from those previously reported for the genus Nothobranchius and similar to the Actinopterygii conservative karyotype.

Molecular identification of a cryptic species in the Amazonian predatory catfish genus Pseudoplatystoma (Bleeker, 1962) from Peru

Pseudoplatystoma species are highly prized South American Pimelodid migratory catfishes. Until recently, their taxonomy was not clearly established, with discrepancies between morphological and molecular analyses. Here, Pseudoplatystoma species from the Peruvian Amazon were characterized at the molecular level from a sample representing the observed range of their color pattern variations in the study area. Analyses were performed using seven microsatellite loci for 103 specimens and, for part of them (52), using sequences of two regions of their mitochondrial genome [Cytochrome Oxidase subunit I (COI) and Control Region (CR)]. Factorial correspondence analysis and assignment tests based on microsatellite polymorphism showed that the specimens originally identified as P. punctifer belonged to two different gene pools highly differentiated from P. tigrinum. Morphological examination identified two different morphotypes (with and without black stripes), suggesting the existence of two distinct taxa within P. punctifer. This result was corroborated by the ML tree based on CR sequences, where all individuals but four clustered in a similar way as in the FCA and Bayesian assignment tests. For these four individuals, mitochondrial introgression or retention of ancestral polymorphism was likely. In contrast, the ML tree based on COI sequences showed that reciprocal monophyly was not yet achieved for this marker for the two P. punctifer taxa. The existence of three sympatric species of Pseudoplatystoma in the Peruvian Amazon is discussed in relation to their molecular characteristics, color patterns and ecology. Evolutionary scenarios regarding their divergence are hypothesized.

Local adaptation to altitude underlies divergent thermal physiology in tropical killifishes of the genus Aphyosemion

In watersheds of equatorial West Africa, monophyletic groups of killifish species (genus Aphyosemion) occur in discrete altitudinal ranges, low altitude species (LA, sea level to ∼350 m) or high altitude species (HA, 350 to 900 m). We investigated the hypothesis that local adaptation to altitude by the LA and HA species would be revealed as divergent effects of temperature on their physiological energetics. Two species from each group (mass ∼350 mg) were acclimated to 19, 25 and 28°C, with 19 and 28°C estimated to be outside the thermal envelope for LA or HA, respectively, in the wild. Wild-caught animals (F0 generation) were compared with animals raised in captivity at 25°C (F1 generation) to investigate the contribution of adaptation versus plasticity. Temperature significantly increased routine metabolic rate in all groups and generations. However, LA and HA species differed in the effects of temperature on their ability to process a meal. At 25°C, the specific dynamic action (SDA) response was completed within 8 h in all groups, but acclimation to temperatures beyond the thermal envelope caused profound declines in SDA performance. At 19°C, the LA required ∼14 h to complete the SDA, whereas the HA required only ∼7 h. The opposite effect was observed at 28°C. This effect was evident in both F0 and F1. Reaction norms for effects of temperature on SDA therefore revealed a trade-off, with superior performance at warmer temperatures by LA being associated with inferior performance at cooler temperatures, and vice-versa in HA. The data indicate that divergent physiological responses to temperature in the LA and HA species reflect local adaptation to the thermal regime in their habitat, and that local adaptation to one thermal environment trades off against performance in another.

[Genetic diversity of Pseudosciaena polyactis in Zhoushan based on mitochondrial DNA D-loop region sequences]

Pseudosciaena polyactis is an economically important species of marine fish in China that is currently declining due to overexploitation, environmental pollution and related factors. Research in to the genetic structure of Pseudosciaena polyactis populations plays a key role in protecting and promoting sustainable utilization. We collected 53 individuals of Pseudosciaena polyactis from Zhoushan, Zhejiang and sequenced and amplified the mitochondrial DNA (mtDNA) D-loop region using Polymerase Chain Reactions (PCR). The sequence length of the 53 individuals ranged from 795 to 801 bp. The sequences were analyzed by Clustal X1.83, MEGA3.1 and DnaSP4.0. The results showed that the average base content of T, C, A, G was 30.3%, 23.1%, 32.3% and 14.3%, respectively and there were 93 transition or transversion sites, including 53 single nucleotide mutation sites and 40 parsimony informative sites, which accounted for 11.6% of the length of the analyzed sequences. In total, we identified 52 haplotypes and found haplotype diversity (hd) of 0.9993, average number of nucleotide differences were 9.73875 (k), and nucleotide diversity (Π) of 0.01233. The average genetic distance of haplotypes was 0.012, and the average transition/transversion was 4.305. Based on mitochondrial DNA D-loop region sequences, these results indicate that the genetic diversity of the Pseudosciaena polyactis population in Zhoushan is currently at a medium level.

Female mating preference for own males on species and population level in Chromaphyosemion killifishes (Cyprinodontiformes, Nothobranchiidae)

Chromaphyosemion killifishes are a very promising taxon for the examination of general principles and mechanisms underlying speciation. The polygamous mating system and high degree of sexual dimorphism in this group suggest that sexual selection and female mating preferences play a crucial role in the current radiation process. Because the emergence of mating preferences for individuals of the own population during allopatry is a necessary precondition for speciation by sexual selection, either via diverging mate recognition traits or reinforcement, we examined whether females of different nominal species (Chromaphyosemion bivittatum vs. Chromaphyosemion volcanum) or populations (C. bivittatum "Toko" vs. C. bivittatum "Ilor") prefer their own males as mating partners. For this purpose, two different methods were used. First, we conducted simultaneous choice tests where females could choose between two different males, and second, we counted the eggs produced by females in consecutive matings with different males. Both approaches produced the same result: females of the populations under examination preferred to mate with their own males. Preference for own males was symmetrical in all tests. Males, on the other hand, do not discriminate between females, not even on the level of nominal species. Thus, our results are in accordance with the hypothesis that female choice is an important factor for speciation in Chromaphyosemion. Additionally, we present some preliminary data on post-zygotic isolation between the populations.