Evolution of sex allocation plasticity and its predictors in a flatworm genus

Local sperm competition (LSC), which occurs when related sperm compete for access to a given set of eggs, can influence sex allocation (SA) in simultaneous hermaphrodites. Different factors that have been predicted to affect LSC—and hence, optimal SA—include the mating strategy (such as reciprocal mating vs. hypodermic insemination) and the ability to self-fertilize. Moreover, the level of LSC experienced could vary temporally and/or spatially, favouring the evolution of SA plasticity. However, it is unknown how the mating strategy and ability to self-fertilize can influence SA and SA plasticity. Here, we explored this by collecting estimates of SA and SA plasticity for seven species of the flatworm genus, Macrostomum, and performing analyses while controlling for phylogeny. While we found substantial interspecific variation in SA, neither the mating strategy nor the ability to self-fertilize had a significant effect on SA. Next, we estimated standardized effect sizes for SA plasticity in response to i) the presence of mating partners and ii) the strength of LSC for each species, and tested if the mating strategy or ability to self-fertilize predicted these effect sizes. We found considerable interspecific variation in SA plasticity, with some species being highly plastic and others showing no significant plasticity. Moreover, self-fertilization predicted SA plasticity with respect to the presence of mating partners, with SA plasticity being lower for self-fertilizing species. Finally, we showed that interspecific variation in SA is nearly three times higher than intraspecific variation, suggesting that SA estimates in field-collected specimens can, at least to some degree, be interpreted as representing interspecific rather than intraspecific variation. Our study suggests that both SA and SA plasticity can evolve rapidly, with self-fertilization being an important predictor for the latter in Macrostomum.

KARAKTERISTIK FENOTIPE DAN GENOTIPE IKAN GURAMI, Osphronemus goramy, STRAIN GALUNGGUNG HITAM, GALUNGGUNG PUTIH, DAN HIBRIDANYA

Persilangan antara dua populasi yang berbeda secara genetik lazimnya menghasilkan kombinasi genetik baru. Penelitian ini dilakukan untuk mengevaluasi karakteristik fenotipe dan genotipe ikan gurami strain Galunggung Hitam, Galunggung Putih, dan Hibridanya. Perkawinan dalam galur (GP X GP dan GH X GH) dan persilangan dua arah antara betina GH dan jantan GP (GH X GP), dan resiprokalnya (GP X GH) telah dilakukan di BPBIGN Singaparna. Fenotipe dianalisis berdasarkan metode truss morfometrik dan meristik, sedangkan karakteristik genotipe diamati menggunakan metode PCR-RAPD. Hasil analisis menunjukkan berdasarkan 21 karakter truss morfometrik, centroid hibrida GH X GP lebih tinggi dari centroid ketiga populasi lainnya pada PC-1 yang dicirikan oleh karakter B3, B4, B5, A3, A4, dan A6, dan bersifat intermediate pada PC-2, PC-3, dan PC-4. Berdasarkan delapan karakter meristik, centroid hibrida GH X GP lebih tinggi dari kedua tetua dan hibrida GP X GH pada PC-1 yang dicirikan oleh karakter SPR dan SDA, lebih rendah dari kedua tetua, tetapi lebih tinggi dari populasi GP X GH pada PC-2, dan lebih rendah dari ketiga populasi lainnya pada PC-3 dan PC-4. Polimorfisme dan heterozigositas pada populasi hibrida GH X GP dan GP X GH lebih tinggi daripada kedua tetuanya GH X GH dan GP X GP. Hibridisasi yang dilakukan meningkatkan variasi genetik yang dapat berguna dalam peningkatan produktivitas budidaya.Hybridization between two genetically different populations is expected to generate a population carrying new genetic combinations which may be expressed in both phenotypes and genotypes. This study was carried out to explore the phenotype and genotype characteristics of reciprocal hybrids of goramy of Galunggung black (GH) and Galunggung white (GP) with respect to their parental lines. Matings within the same line producing GP X GP and GH X GH, and reciprocal mating producing hybrids GH X GP and GP X GH, were conducted at BPBIGN Singaparna. Samples representing the four populations were analyzed for their morphology using truss morphometric and meristic methods, while genotypes were analyzed using PCR-RAPD method. The results showed that based on the 21 morphometric characters, the centroid of hybrid GH X GP was higher than those of the other three populations at PC-1, which was marked by the characters B3, B4, B5,A3, A4, and A6, and was intermediate at PC-2, PC-3, and PC-4. Based on the eight meristic characters, the centroid of GH X GP was also higher than those of their parents and hybrids GP X GH at PC-1, which was marked by the characters SPR and SDA, lower than those of their parents but higher than that of hybrid GP X GH at PC-2, and lower than those of the other three populations at PC-3 and PC-4. The genetic diversities in terms of polymorphism and heterozygosity levels in hybrids GH X GP and GP X GH were higher than those found in the pure-line (GH X GH and GP X GP). Hybridization conducted in this study had resulted in the enhancement of genetic variations which could be useful in increasing aquaculture productivity.

A mechanism aiding simultaneously reciprocal mating in snails

The majority of hermaphroditic animals mate on a given occasion as either male or female, but terrestrial snails and slugs generally mate reciprocally with each partner participating in both sexual roles. This manner of mating requires that the genitalia be exactly opposed prior to copulation attempts, a task made difficult in snails and slugs by the absence of hearing and very limited vision. In the brown garden snail, Cornu aspersum (Müller, 1774), we found that a small protruding structure associated with the genital atrium plays an important role in positioning the snails prior to copulation. Lesions of the penial lobe reduced mating success rates, delayed mating, increased the number of attempted intromissions, and increased the number of unilateral intromissions. The sensory capacity of the penial lobe is demonstrated by histological and electrophysiological evidence, and behavioral data suggest that the lobe is also a stimulus for the partner snail. A literature review suggests that structures functionally equivalent to the penial lobe may be present in many gastropod molluscs that mate simultaneously and reciprocally, but in none that mate in other ways.

Asymmetric reproductive isolation during simultaneous reciprocal mating in pulmonates

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.

HIGH MUTABILITY IN MALE HYBRIDS OF DROSOPHILA MELANOGASTER

ABSTRACT The frequencies of sex-linked lethal mutations arising in hybrid male offspring from various crosses and in nonhybrid controls were determined. The hybrids were produced by crossing representative strains of the P-M system of hybrid dysgenesis in all possible combinations. Males from the cross of P males × M females had a mutation rate about 15 times higher than that of nonhybrid males from the P strain. Genetically identical males from the reciprocal cross had a mutation rate 3 to 4 times that of the nonhybrids. For crosses involving a Q strain, a significant increase in the mutation rate was detected in males produced by matings of Q males with M females. No increase was observed in genetically identical males from the reciprocal mating. Crosses between P and Q strains gave male hybrids with mutation rates not different from those of nonhybrids. Many of the lethals that occurred in hybrids from the cross of P males × M females appeared to be unstable; fewer lethals that arose in hybrids from the cross of Q males × M females were unstable. The relationship between P and Q strains is discussed with respect to a model of mutation induction in dysgenic hybrids.

CYTOPLASMIC INCOMPATIBILITY AND BREEDING ISOLATION IN BARK BEETLES (COLEOPTERA: SCOLYTIDAE)

Unequal fertility of reciprocal crosses between certain bark beetles and increased fertility of the F1, with respect to the original cross, appear to result from nuclear-controlled cytoplasmic incompatibility. This mechanism, also implicated in instances of reciprocal mating sterility, may be an important factor in the reproductive isolation of closely related species.

Associations between serum transferrin polymorphism and disturbed segregation ratios in Welsh Mountain sheep

Six serum transferrins have been found amongst 1,030 sheep in a Welsh Mountain sheep flock, apparently produced by six genes segregating as alleles at a single locus. All 21 possible phenotypes have been found.The genes are designated TfA, TfB, Tfc, TfD, TfE and Tfp, TfA producing the fastest, and Tfp, the slowest migrating component. TfE and Tfp are at a much lower frequency (0·01 to 0·06) than the remaining genes (0·2 to 0·3) and Tfp may represent a fifteenth allele at this locus.A comparison of observed phenotype frequencies with those expected under random mating, showed that a marked disturbance in segregation existed, with homozygous TfCC animals in consistent excess and a marked shortage of heterozygous TfBC and TfCD animals. Variation amongst remaining phenotypes appeared to be at random. However, incompatibility with the Tfc gene also extended to matings including Tfp. Examination of 282 matings confirmed that the effect of the Tfc gene favours maternal-foetal incompatibility as a cause of disturbed segregation, rather than selective fertilisation. However, reciprocal mating data were not available.