Bottlenecks, drift and differentiation: the fragmented population structure of the saltmarsh beetle Pogonus chalceus.

We investigated the distribution of genetic variation within and between 10 fragmented populations of the saltmarsh beetle Pogonus chalceus in the region of Flanders (Belgium) representing all extant populations of the species in that region by using allozyme and microsatellite markers. Beetle population size and habitat area failed to explain a significant part of the genetic variability. Microsatellite allelic diversity was sensitive to population size differences but not to saltmarsh area estimates. Heterozygosities of both marker types and allozyme allelic diversity on the other hand showed no significant correlation to population size and saltmarsh area. There was also no correlation between geographical and genetic distances among populations. Evidence was found for past bottlenecks in some of the smallest populations. Maximum likelihood methods using the coalescent approach revealed that the proportion of common ancestors was also high in those small populations. 35% of our studied individuals, especially in the largest populations showed a relative wing size smaller than 70%. Moreover, only six out of the 10 studied populations showed a few individuals with functional flight musculature. In conclusion, the overall pattern of distribution of genetic variation and the low flight capacity did not support an equilibrium model of population structure in P. chalceus, but mainly suggested a lack of regional equilibrium with both drift and gene flow influences.

Genetic differentiation among populations of the salt marsh beetle Pogonus littoralis (Coleoptera: Carabidae): a comparison between Atlantic and Mediterranean populations.

Genetic differentiation was studied among populations of the salt marsh beetle Pogonus littoralis (Coleoptera: Carabidae), comparing Atlantic and Mediterranean populations over a large part of its range. The genetic structure of this highly mobile beetle was investigated by studying allozyme polymorphism at nine enzyme loci in 13 populations. Mediterranean P. littoralis were highly significantly differentiated from Atlantic populations. Moreover, more isolated Atlantic populations showed increased differentiation and decreased genetic diversity compared to less fragmented Mediterranean populations.

Genetic differentiation and local adaptation in the salt-marsh beetle Pogonus chalceus: a comparison between allozyme and microsatellite loci.

The genetic structure of Pogonus chalceus from 11 Atlantic and seven Mediterranean Western European populations was analysed. Results from seven allozyme loci were compared to five microsatellites to test the hypothesis that some enzymatic loci undergo selection. Both allozyme and microsatellite results showed that Mediterranean beetle populations are genetically distinct from Atlantic populations. The analysis of the genetic structure showed that FST values derived from all microsatellite loci were much smaller than those obtained from allozymes. The enzymatic locus Idh-1 exhibited a high value compared to the other loci, suggesting that it is non-neutral. The same Idh-1 locus was implicated in differentiation between temporary and stable populations, as followed also from a highly significant relationship between the allele two of this Idh-1 locus and dispersal power population estimates. The 'parallel evolution' model may account for the diversification of locally adapted Pogonus chalceus populations between different microhabitats.

Mechanisms of branchial cartilage growth in Astatotilapia elegans (Teleostei: Cichlidae).

The growth of the cartilaginous infrapharyngobranchial II (part of the upper pharyngeal jaws) in the cichlid fish Astatotilapia elegans was investigated in four successive early postembryonic stages. Total cell number, individual cell volumes, total cell, total matrix and total cartilage volume were accurately measured or calculated. The share of cell and matrix volume increase in the overall growth was calculated for each of the transitions. Matrix volume increase accounted for almost 60% of the overall rudiment increase. Non-hypertrophic cells and the matrix produced by them together accounted for about three quarters of the total cartilage volume increase. Zones with particular characteristics (cell orientation, cell shape, degenerative features, etc.) were distinguished in each of the four stages separately. The sequence of increasing mean cell volume between zones was interpreted as reflecting growth directions within the cartilage. Apposition probably largely contributed to the observed cell volume increase. Mean cell volume and mean matrix volume per cell showed a highly significant positive relation. Cell density showed a highly significant negative relation to both mean cell volume and mean matrix volume. Our results indicate that the area of hypertrophy and cartilage resorption may be established quite early in the rudiment before overt manifestation of these processes.