An ecomorphological framework for the coexistence of two cyprinid fish and their hybrids in a novel environment

Niche variation between hybrid taxa and their parental species has been deemed imperative to the persistence of hybrid populations in nature. However, the ecological factors promoting hybrid establishment remain poorly understood. Through the application of a multidisciplinary approach integrating genetics, morphometry, life‐history, and trophic ecology, we studied the hybrids of roach (Rutilus rutilus L.) and bream (Abramis brama L.), and their parental species inhabiting an Irish lake. The roach × bream hybrid exhibited a body shape intermediate of that of the parental species. Diet analyses depicted the hybrid as a generalist, feeding on all prey items consumed by either parental species. Stable isotope data confirm the trophic niche breadth of hybrids. A significant correlation between body shape and diet was detected, suggesting that the intermediate phenotype of hybrids might play a role in their feeding abilities, resulting in the utilization of a broader trophic spectrum than the parental species. Growth and age class structure analyses also yielded a scenario that is consistent with the ecological success of hybrids. Genetic analyses suggest that the majority of hybrids result from first‐generation crosses between the parental species; however, a potentially significant proportion of back‐crosses with bream were also detected. The recent introduction of roach and bream into Irish waters, as well as the climatic and ecological features of the colonized habitats, can explain the remarkable success of the roach × bream hybrid in Ireland. The adaptive significance of hybridization and its demographic consequences for the parental species are discussed. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 768–783.     

Allozymic and morphometric analysis of populations in the Zygaena purpuralis complex (Lepidoptera, Zygaenidae)

In Central Europe and Asia Minor Zygaena purpuralis and Z. minos are two sibling species exhibiting a considerable geographic variation in several features. In this study we examine some populations from the Central and Southern Apennines (Italy) by comparing multivariate analyses of individual allozymic multilocus profiles and of individual morphometric profiles of male genitalia in order to assess their genetic and phenetic relationships.
Results indicate that populations of Z. purpuralis in the Apennines behave in rather different ways with respect to the occurrence of gene exchange with other gene pools. No gene flow appears to occur between two geographically close southern populations; however, extensive introgression, revealable at both the allozymic and morphometric level, seems to occur between some purpuralis and minos -like sympatric populations from Abruzzi. Evolutionary relationships among these peninsular Italy populations are discussed with reference to historical factors, that is, the occurrence of multiple Pleistocene refugia, which could have determined different degrees of isolation among gene pools. This situation is rather different from that previously outlined for Central Europe and present results suggest that the Z. purpuralis complex might include more than two biological species.     

Sero-systematic and taximetric studies on the Phaseoleae (Fabaceae) and related tribes

VIVIANI, T., CONTE, L., CRISTOFOLINI, G. & SPERANZA, M., 1991. Sero-systematic and taximetric studies on the Phaseoleae (Fabaceae) and related tribes. One hundred and fifty-two species of Phaseoleae, Desmodieae, Indigofereae, Millettieae, Sophoreae and Swartzieae were subjected to a taximetric study. The serological relationships were analysed using 37 antigenic systems and 12 antisera upon a representative sample from the six tribes. The comparative use of taximetric and serological data allowed the following conclusions to be drawn: (1) the tribe Phaseoleae is not a natural taxon; the primitive complex Diocleinae-Glycininae, the more derived Phaseolinae, and the Cajaninae deserve tribal rank; the position of the remaining subtribes requires further examination. (2) The Desmodieae are related to the Phaseoleae, whereas the Indigofereae have little relation to them. (3) The Baphia -group in the Sophoreae is possibly related to the Phaseoleae ancestors, while the other Sophoreae belong to different phyletic lines. (4) Swartzia is morphologically related to the Sophoreae, but does not belong to the same natural group. (5) Sophoreae, Millettieae and Phaseoleae are three heterogeneous aggregates representing stages of increasing specialization, rather than elements of a single phyletic line.     

MHC heterozygosity and survival in red junglefowl

Genes of the major histocompatibility complex (MHC) form a vital part of the vertebrate immune system and play a major role in pathogen resistance. The extremely high levels of polymorphism observed at the MHC are hypothesised to be driven by pathogen‐mediated selection. Although the exact nature of selection remains unclear, three main hypotheses have been put forward; heterozygote advantage, negative frequency‐dependence and fluctuating selection. Here, we report the effects of MHC genotype on survival in a cohort of semi‐natural red junglefowl (Gallus gallus) that suffered severe mortality as a result of an outbreak of the disease coccidiosis. The cohort was followed from hatching until 250 days of age, approximately the age of sexual maturity in this species, during which time over 80% of the birds died. We show that on average birds with MHC heterozygote genotypes survived infection longer than homozygotes and that this effect was independent of genome‐wide heterozygosity, estimated across microsatellite loci. This MHC effect appeared to be caused by a single susceptible haplotype (CD_c) the effect of which was masked in all heterozygote genotypes by other dominant haplotypes. The CD_c homozygous genotype had lower survival than all other genotypes, but CD_c heterozygous genotypes had survival probabilities equal to the most resistant homozygote genotype. Importantly, no heterozygotes conferred greater resistance than the most resistant homozygote genotype, indicating that the observed survival advantage of MHC heterozygotes was the product of dominant, rather than overdominant processes. This pattern and effect of MHC diversity in our population could reflect the processes ongoing in similarly small, fragmented natural populations.     

Patterns of Amazonian area relationships based on raw distributions of papilionid butterflies (Lepidoptera: Papilioninae)

Diversifications within a biota are due to several factors. Although some of these are untestable with current analytical methods, hierarchical congruence obtained with different cladistic methods and based on independent taxa are undoubtedly important. In the recent past, most hypotheses of historical biogeography (e.g. refugial, riverine, disturbance, vicariance) were tested on the Amazonian biota, selecting a number of diverse organisms such as plants, anurans, lizards, butterflies, birds and monkeys. In this study we used parsimony analysis of endemicity to infer historical relationships among 16 interfluvial areas in the Amazonian lowlands based on raw distributions of 114 Papilioninae (Lepidoptera). The analysis yielded two most parsimonious trees of area relationships. One tree was characterized by two main clusters of areas which showed a separation of Guyanan + south-east Amazonian interfluvial areas from western Amazonian interfluvial areas. The second tree showed the Guyanan interfluvial areas basal to a cluster which included all the other interfluvial areas. This latter cluster was subdivided into two main groups of areas separating the south-east Amazonian and the western Amazonian interfluvial areas. This result is discussed in the light of previous hypotheses obtained with the same method using some vertebrate taxa in the Amazonian lowlands. Likewise, comparisons with other hypotheses on lineages of birds, mammals and butterflies obtained applying cladistic biogeographical methods are made. The two alternative vicariant patterns presented for papilionid butterflies are strictly congruent with those for birds.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 345–357.