Analysis of mitotic karyotypes of wild specimens of larvae of the Bactmcera tau-like fruit flies (Diptera: Tephritidae) in Thailand has revealed seven distinct chromosome forms, based on the amount and distribution of heterochromatin in sex chromosomes and autosomes. Such cytological differences are perfectly correlated with morphological observations and molecular genetics data. These findings clearly suggest that B. tau is a cluster of at least seven closely related species temporarily designated as species A (= B. tau), B, C, D, E, F and G. On the basis of the gross quantity of heterochromatin accumulation in the genome, three groups of mitotic karyotypes can be recognized. Group 1 comprises species A and E. Species E specifically occurs only in fruits of Shychnos thorelii while species A attacks many kinds of host plants. Group 2 contains species B, F and G. Species B has been found only in Siphonodon celastrineur fruit, whereas species F and G attack the same host species, the medically important plant, Hydnocarpus anthelminthicus, albeit in different localities. Group 3 includes species C and D, each of which comprises larger amounts ofpericentric heterochromatin in all chromosomes than the other two groups. Hence, these two species are cytologically remote from those of groups 1 and 2. Species C and D occur allopatrically but they attack the same host plant species, Momordica c0chinchinenSi.s. Thus, genetic differentiation at the chromosomal level to specific host plant species and geographic isolation seem to play an important role in speciation of members of the B. tau complex. 0 2000 The Linnean Society of London ADDITIONAL KEY WORDS:-Bachocera tau complex -metaphase chromosome heterochromatin -karyotypic evolution.

Summary Wild samples of larvae of 6 new fruit fly species belonging to the Bactrocera dorsalis complex have been temporarily designated as species I, J, K, L, M and N, based on cytological evidence. The flies are also morphologically distinguishable as adults. The larvae of these species seem to specifically infest fruits of different host plants. Cytological examination of larvae of these new species has revealed distinct patterns of metaphase karyotypes on the basis of different amounts and distribution of constitutive heterochromatin in sex chromosomes and autosomes. Thus the mitotic karyotype of species I is somewhat similar to that of B. dorsalis and is classified into Group 1. On the other hand, species L, M and N exhibit mitotic karyotypes of Group 4 showing specific patterns of heterochromatin in the centromeric regions of the X chromosome. Species J and K show a general feature of the mitotic karyotype of Group 3, which exhibits distinctive patterns of heterochromatin in sex chromosomes. These findings support the important role of constitutive heterochromatin in karyotypic evolution of these members of the B. dorsalis complex. Such a gross difference in heterochromatin is also a useful tool in cytotaxonomic study of closely related species of the fruit flies of Thailand.

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Population genetics has been recognized as a key component of policy development for fisheries and conservation management and aquaculture development. This study aims to evaluate the genetic diversity and population structure of native cobia (Rachycentron canadum) in the Gulf of Thailand and Andaman Sea, establishing the existing population distributions and contributing information to aid in the development of policy, prior to extensive aquaculture development. Microsatellite analysis of natural cobia populations in these two ocean basins shows similar levels of gene diversity at 0.844 and 0.837, respectively. All populations and almost all microsatellite loci studied show significant heterozygote deficiency. Genetic differentiation between local populations is low and mostly not significant (R ST = -0.0109 to 0.0066). The population shows no marked structure over the long geographic barrier of the Thai-Malay peninsula, either when analyzed using pairwise genetic differences or evaluated without predefined populations using STRUCTURE. Additionally, a Mantel test shows no evidence of isolation by distance between the population samples. The significant heterozygote deficiency at most of the loci studied could be explained by the possibility of null alleles. Alternatively, given the behavior of forming small spawning aggregations, seasonal migration, and hitchhiking on large marine animals, the population genetics could be complex. The population of cobia at each location in Thai waters may be inbred, as a result of breeding between relatives, which would reduce heterozygosity relative to Hardy-Weinberg frequencies, while some of these populations could be making long distance migrations followed by admixture between resident and transient groups. This migration would cause population homogeneity in allele frequencies on a larger geographic scale. The results suggest that 123Aquacult Int (2013( ) 21:197-217 DOI 10.1007 fisheries management for this species should be considered at both national and international levels, and until the possibility of local adaptation is fully investigated, policy development should apply the precautionary principle to ensure the preservation of genetic diversity and the sustainability of local and regional fisheries.

Homeotic genes, which function to specify segment identity along the anterior-posterior axis of embryos, are controlled by extensive batteries of enhancer sequences. We have investigated patterns of interspecific and intraspecific molecular variation in three enhancers of the Ultrabithorax (Ubx) locus, which are bx-32.8, pbx32.7, and bxd4.1, from the Drosophila melanogaster species group. These enhancer sequences control Ubx expression by binding to multiple transcription factors encoded by gap, pair-rule, and dorsoventrally expressed genes. Sequence comparisons reveal purifying selection acting on all three enhancers, both in bases binding transcription factors and in bases whose functions are as yet unknown. Neutrality tests largely fail to reject a neutral evolution model. However, using a matrix similarity value to reflect the binding affinity of the protein-binding sites, interspecific and intraspecific variation that may have potential to affect the binding affinity of the sequences homologous to those binding transcription factors in D. melanogaster are discovered, suggesting evolutionary flexibility in the way in which these sequences function in the control of development. As a means of measuring the impact of intraspecific variation on observable phenotypes, we have induced Ubx mutant phenocopies with embryonic ether treatment, and find strong and highly significant variation between D. melanogaster strains in their phenocopy frequencies. This variation shows no significant correlation with the strengths of the mutant phenotypes when the strains are heterozygous with a Ubx null mutation. Estimated phylogenetic trees have been constructed for the three enhancer regions investigated. Neither of the two phenotypic traits investigated shows any significant associations with the phylogeny of any of the three enhancers.