Traditional taxonomy of shell-bearing molluscs does not generally use soft-body coloration. However, the land snails Bradybaena pellucida and B. similaris have been distinguished only on the basis of the color of the soft-body visible through the shell. Thus, the taxonomic status of the two species has traditionally been questionable. We found that dense spots of pigments embedded in the dorsal mantle are responsible for the yellow coloration of B. pellucida . Similar spots in B. similaris are white and less densely aggregated in whorls further from the apex, and the brown color of the hepatopancreas is visible through the shell. The yellow pigments of B. pellucida seep out with mucus from the body in natural and laboratory conditions. The two species became externally indistinguishable after 30 days of laboratory feeding, because the yellow spots disappeared in B. pellucida and the color of the hepatopancreas changed from dark brown to pale brown in both species. Irradiation with ultraviolet A demonstrated that the yellow pigment of B. pellucida fluoresces. Adult specimens of the two species were distinct in penial microsculpture, with F(1) hybrids intermediate in form. Populations of the two species differed significantly in allelic frequencies at four allozyme loci. Therefore, B. pellucida and B. similaris are morphologically and genetically distinct. The fluorescent yellow pigment distinguishes B. pellucida from B. similaris under natural conditions despite its environmental dependence.

The generality of asymmetric reproductive isolation between reciprocal crosses suggests that the evolution of isolation mechanisms often proceeds in reciprocal asymmetry. In hermaphroditic snails that copulate simultaneously and reciprocally, asymmetry in premating isolation may not be readily detectable because the failure of the symmetric performance of courtship would prevent copulation from occurring. On the other hand, through their prolonged copulation, snails discriminate among mates when exchanging spermatophores for their benefit and thus may exhibit asymmetric reproductive isolation during interspecific mating. However, no clear case of reciprocal asymmetry has been found in reproductive isolation between snail species. Here we show a discrete difference in hybridization success between simultaneous reciprocal copulations between two species of pulmonate snails. Premating isolation of Bradybaena pellucida (BP) and Bradybaena similaris (BS) is incomplete in captivity. In interspecific copulation, BP removes its penis without transferring a spermatophore, while BS sires hybrids by inseminating BP. Thus, 'male' BP or 'female' BS rejects the other individual, while female BP and male BS accept each other, so that the two sexes of either BP or BS oppose each other in mate discrimination. Our results are a clear example of asymmetry in reproductive isolation during simultaneous reciprocal mating between hermaphroditic animals.

Depending on fitness consequences, hybridization may rescue inbred populations; generate premating barriers, reproductive interference, or hybrid species; or extinguish a species. However, the fitness of hybrids is unpredictable without direct quantification of their performance in fitness components across multiple generations. The land snails Bradybaena pellucida and B. similaris, which are indigenous and non-indigenous in Japan, respectively, copulate with each other simultaneously and reciprocally. However, only B. pellucida produces hybrids, because it ends mating by removing the penis before transferring a spermatophore, while B. similaris inseminates B. pellucida. To evaluate the strength of an intrinsic postzygotic barrier against the hybrids produced by B. pellucida, we conducted breeding experiments in the laboratory and measured six life-history traits: (1) growth rate, (2) body weight at maturity, (3) number of days to first oviposition after being permitted to mate, (4) clutch size, (5) fecundity, and (6) hatchability. We also calculated the relative intrinsic fitness based on five of these trait values (excluding clutch size). F1 hybrids exhibited heterosis in growth rate, body weight at maturity and relative intrinsic fitness. F2 hybrids also showed heterosis in body weight at maturity. Nevertheless, the F2 hybrids produced significantly fewer progeny than the mid-point value of the parental species. Thus, the F2 hybrids exhibited weak outbreeding depression in reproduction, offsetting their vigor in body size. These results indicate that only a weak postzygotic barrier, contrasting with strong F1 heterosis, has evolved during genetic divergence of the two sibling species in allopatry.

The eastern sarus crane, Grus antigone sharpii, is distributed in the Indochina area, though it has become extinct in Thailand. The Thai government has tried to repopulate the cranes using wild individuals from Cambodia as initial breeding stock. Although captive breeding can reintroduce species back into the wild, the genetic diversity of the population is also important. This study aimed to screen microsatellite markers to investigate the genetic diversity of G. a. sharpii from two breeding facilities in Thailand and to assess its potential for future conservation programs. Eighteen microsatellite loci isolated from whooping crane (G. americana) and blue crane (Anthropoides paradisea) were screened in all captive reared cranes from Khao Kheow Open Zoo (n = 11) and Bangpra Water Bird Breeding Station (n = 17), Chonburi Province. Of 18 loci analyzed, 14 were found to be polymorphic, and 3 loci were in linkage disequilibrium. Apparent deviation from Hardy-Weinberg equilibrium was observed only at locus Gram8, resulting from the presence of a null allele. The average expected and observed heterozygosities from 10 loci analyzed are 0.61 and 0.64, respectively. The overall fixation index suggested that cranes from both facilities shared many common alleles (F = 0.023, p < 0.05); in addition, Bayesian clustering analysis implied that cranes from two breeding facilities are homogeneous (K = 1). Our findings reveal high level of genetic diversity of the captive crane population in Thailand and suggest that the breeding stocks may be suitable for ensuring a sustainable breeding program in the future.

The Crustacean hyperglycemic hormone (CHH) has been shown to exist as multiple molecular forms in several crustacean species. In Penaeus monodon, a gene encoding CHH (so-called Pem-CHH1) was recently described. In this study, the molecular structures of two other CHH genes (Pem-CHH2 and Pem-CHH3) are reported. Both the Pem-CHH2 and Pem-CHH3 genes contain three exons that are separated by two introns that are similar to the structure of other genes in the same family. An analysis of the upstream nucleotide sequences of each Pem-CHH gene has identified the putative promoter element (TATA box) and putative binding sites for several transcription factors. The binding sites for CREB, Pit-1, and AP-1 were found upstream of all three Pem-CHH genes. A Southern blot analysis showed that at least one copy of each Pem-CHH gene was located within the same 10 kb genomic DNA fragment. These results suggest that the CHH genes are arranged in a cluster in the genome of P. monodon, and that their expression may be modulated by similar mechanisms.