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The spatial scale of dispersal in coral reef fishes eludes ecologists despite the importance of this parameter for understanding the dynamics of ecological and evolutionary processes. Genetic isolation by distance (IBD) has been used to estimate dispersal in coral reef fishes, but its application in marine systems has been limited by insufficient sampling at different spatial scales and a lack of information regarding population density. Here, we present an analysis of IBD in the barred hamlet (Hypoplectrus puella, Serranidae) at spatial scales ranging from 10 to 3200 km complemented with SCUBA surveys of population densities covering 94 000 [m.sup.2] of reef. We used 10 hypervariable DNA markers to genotype 854 fish from 15 locations, and our results establish that IBD in H. puella emerges at a spatial scale of 175 km and is preserved up to the regional scale (3200 km). Assuming a normal or a Laplace dispersal function, our data are consistent with mean dispersal distances in H. puella that range between 2 and 14 km. Such small mean dispersal distances is a surprising result given the three-week pelagic larval duration of H. puella and the low level of genetic structure at the Caribbean scale (Wright's fixation index, FST, estimate = 0.005). Our data reinforce the importance of considering population density when estimating dispersal from IBD and underscore the relevance of sampling at local scales, even when genetic structure is weak at the regional scale. Key words: barred hamlet; connectivity; coral reef fishes; demography; dispersal; Hypoplectrus puella; isolation by distance; marine; pelagic larvae; population genetics; spatial scale.

Studies empirically demonstrate an important aspect of habitat specific mating bearing directly on sympatric host race formation and specification of phytophagous insects. The implications of non-natal fruit avoidance for the evolutionary dynamics and genetics of sympatric speciation are discussed.

A three-tiered genetic analysis of egg-to-adult development time and viability in ancestral and derived populations of cactophilic Drosophila mojavensis was performed to study the divergence in life-history characters and correlated shifts in sexual isolation among geographically isolated populations of D. mojavensis. The regional shifts observed in life history evolution once D. mojavensis invaded mainland Mexico from Baja California by shifting host plant was genetically correlated with variation in cuticular hydrocarbon-based mate preferences.

A total of 34 loci distributed along the X chromosome and chromosome 14 were resequenced to assess the significance of the X chromosome in reproductive isolation between subspecies of the European rabbit and to study the genomic scale over which islands of differentiation extend. The results confirmed the significant role of the X chromosome in the reproductive isolation between rabbit subspecies and demonstrated the mosaic nature of the genome at species boundaries.

An experimental test was conducted to examine the behavioral discrimination in North Island (NI) saddlebacks Philesturnus rufusafer exposed to familiar and unfamiliar male rhythmical song (MRS) and determine the divergence of conspecific recognition signals (CRS) among isolated populations. The obtained results demonstrated the rapid tempo with which discrimination of CRS might evolve within isolated populations and supported both bottleneck and cultural mutation hypotheses in CRS evolution.

The statistical approach to test the significance of phylogeographic subdivisions and assess the power to detect the genetic isolation by distance pattern was used to understand the specific case of hydrothermal vent invertebrates. The low statistical power associated with the sampling effort explained the failures to detect evidence for isolation-by-distance (IBD) and the simulation methods proposed could also find potential application for testing the significance of inferred phylogeographic gaps in other species.

The studies related to the evolutionary history of a controversial hybrid Narcissus xpereziarae and the origin of orphan hybrid populations of N. xpereziarae in eastern Spain, hundreds of kilometers away from N. cavanillesii are presented. The findings offer insight into the low-reproductive barriers to fertilization by foreign pollen in N. cavanillesii, molecular footprints of the former presence of this species in the area and active asexual propagation by bulbs in N. xpereziarae, and overlapping ecological niches.

The taxidermic mount presentation and song playback experiments are used to assess the relative roles of divergent song and color in homotypic ('same type') recognition between one pair of diverged sister taxa of flycatcher, chestnut-bellied Monarcha c. castaneiventris and the white-capped M.c. richardsli forms). The differences in plumage and song used in homotypic recognition revealed the significance of multimodal signal divergence in the evolution of premating reproductive isolation.

Several theoretical and analytical studies are conducted to explain the characteristics and the causes of the partial sexual isolation that exists between the US and the Caribbean Drosophila melanogaster. The observed isolation is shown to be a combined result of the African morphology, behavior and phermones.

The studies employ the analysis of the intrinsic rate of increase to determine the lifetime fitness in two different generations of Ipomopsis hybrids, namely Ipomopsis aggregata and Ipomopsis tenuituba. The cytoplasmic effects and the genotype-by-environment interactions are shown to be extremely important in lowering the hybrid fitness.

The population genetics of 576 song sparrows from 23 populations using seven microsatellite loci is examined to assess genetic differentiation among populations and to estimate the effects of drift and immigration on each population. It is suggested that geographic isolation and limited gene flow facilitated by migratory behavior are responsible for maintaining levels of differentiation among Pacific coastal sparrow populations.

The impact of different flight timing and assortative mating on the mechanisms of reproductive isolation (RI) existing between an ant species of hybrid origin and one of its parents is discussed. A combination of two typical prezygotic and postzygotic mechanisms is shown to contribute to the observed RI.

The various effects of reproductive compensation, gamete discounting, as well as the reproductive assurance on mating-system diversity in hermaphrodites are discussed. The stable mating strategy is shown to be highly affected by the fitness consequences of different family compositions.

Several studies were conducted to explain the effect of sexual selection on speciation, one of the major forces facilitating the reproductive isolation. Sexual selection is found to highly affect speciation and other processes, including ecological selection and the selection for species recognition.

The patterns of reproductive isolation of the tungara frog 'Physalaemus pustulosus' in Costa Rica and Panama are assessed. It was observed that the northern and southern tungara frogs have diverged genetically and bioacoustically and that significant differences in sexual signals are not always correlated with strong genetic differentiation.