Drosophila ananassae: a species characterized by spontaneous male recombination in appreciable frequency

Mutation and recombination are primarily responsible for generating the genetic variability in natural populations of microorganisms, plant and animal species including humans. Upon such genetic variations, elemental forces of evolution such as natural selection, random genetic drift and migration operate to bring about micro-evolutionary changes. Recombination or crossing-over produces new combinations of genes due to interchange of corresponding segments between nonsister chromatids of homologous chromosomes, thus, it is an important evolutionary factor. Since the time of T. H. Morgan, Drosophila has been subjected to extensive investigations on crossing over while employing a number of markers, which were used for gene mapping. Interestingly, recombination occurs in females of D. melanogaster but not in males. Later on, male crossing over was investigated in various species and its occurrence was reported in D. melanogaster, D. ananassae, D. simulans, D. willistoni, D. littoralis and D. bipectinata. Recombination occurs at very low rate in all these species except for D. ananassae, which shows spontaneous male crossing over in appreciable frequency, which is meiotic in origin. This unusual phenomenon in D. ananassae is influenced by various genetic factors as well as it shows strain variation as far as frequency of male recombination is concerned. Further, the presence of chiasmata during meiosis in males at a frequency capable of accounting for the observed recombination frequency extends evidence for meiotic origin of recombination in males of D. ananassae.

Influence of age on mating propensity in two sibling species, Drosophila ananassae and D. pallidosa

Mating propensity in Drosophila is affected by a number of factors including age of flies. Here, we studied the age factor in two sibling species of Drosophila. We tested the effect of age on mating propensity of two sibling species (Drosophila ananassae and D. pallidosa) using five wild type strains of D. ananassae and three wild type strains of D. pallidosa. To determine the effect of age on mating propensity, five age groups were selected: 4, 8, 12, 16 and 20 days of each strain of D. ananassae and D. pallidosa. Fifteen pairs of flies were introduced into the Elens-Wattiaux mating chamber for direct observation for 60 min and in each strain, five replicates were run. Data were analyzed by one-way, two-way ANOVA and student’s t-test. Mating propensity of all the strains of both the sibling species vary significantly. All the strains of both the sibling species showed increase in the mating propensity with age (up to 12 days) and then it decreased as the age prolonged suggesting that 12 days aged flies are more eager to mate. Age wise variation was more pronounced than strain wise variation in D. ananassae. However, it was just opposite in the case of D. pallidosa. Mating propensity of D. ananassae was significantly higher as compared to D. pallidosa in each age group.

Mating latency, duration of copulation and fertility in four species of the Drosophila bipectinata complex.

Significant interspecific variations in mean duration of copulation and fertility were observed in four species of the Drosophila bipectinata species complex. However, D. bipectinata showed positive correlation between duration of copulation and fertility. Similarly, D. malerkotliana showed negative correlation between mating latency and duration of copulation. Likewise, D. pseudoananassae showed positive correlation between mating latency and fertility. These results suggest that D. pseudoananassae has distant relatedness from the other three species with respect to mating latency, duration of copulation and fertility which supports the previous findings.

Behavioural reproductive isolation and speciation in Drosophila.

The origin of premating reproductive isolation continues to help elucidate the process of speciation and is the central event in the evolution of biological species. Therefore, during the process of species formation the diverging populations must acquire some means of reproductive isolation so that the genes from one gene pool are prevented from dispersing freely into a foreign gene pool. In the genus Drosophila, the phenomenon of behavioural reproductive isolation, which is an important type of premating (prezygotic) reproductive isolating mechanisms, has been extensively studied and interesting data have been documented. In many cases incomplete sexual isolation has been observed and the pattern and degree of isolation within and between the species have often been used to elucidate the phylogenetic relationships. The present review documents an overview of speciation mediated through behavioural incompatibility in different species groups of Drosophila with particular reference to the models proposed on the basis of one-sided ethological isolation to predict the direction of evolution. This study is crucial for understanding the mechanism of speciation through behavioural incompatibility and also for an understanding of speciation genetics in future prospects.

Drosophila ananassae: A good model species for genetical, behavioural and evolutionary studies.

Drosophila ananassae, a cosmopolitan and domestic species, was first described by Doleschall in 1858 from Indonesia. During 1930s, cytological and genetical investigations in D. ananassae were initiated in Japan and USA which showed that it is a genetically unique species. Since then a large number of studies have been carried out by researchers in Japan, USA, India, France and Germany in this genetically unique species. Present review briefly summarizes the work done on genetical, behavioural and evolutionary aspects in D. ananassae which demonstrates that it is a good model species for such studies. Further, it is also discussed how the work on D. ananassae has enriched our understanding of basic phenomena like evolution and behaviour compared to similar studies on other model Drosophilds like D. melanogaster, D. pseudoobscura or D.subobsura.

Coexistence of three different Drosophila species by rescheduling their life history traits in a natural population.

We present evidence for coexistence of three different Drosophila species by rescheduling their life history traits in a natural population using the same resource, at the same time and same place. D. ananassae has faster larval development time (DT) and faster DT(egg-fly) than other two species thus utilizing the resources at maximum at both larval and adult stages respectively. Therefore, D. ananassae skips the interspecific competition at pre-adult stage but suffers more from intraspecific competition. However, D. melanogaster and D. biarmipes have rescheduled their various life history traits to avoid interspecific competition. Differences of ranks tests for various life history traits suggest that except for DT(egg-pupa), the difference of ranks is highest for the combination of D. melanogaster and D. ananassae for all other life history traits. This difference is maintained by tradeoffs between larval development time and pupal period and between pupal period and DT(egg-pupa) in D. ananassae.

Female remating, sperm competition and sexual selection in Drosophila

Female remating is fundamental to evolutionary biology as it determines the pattern of sexual selection and sexual conflict. Remating in females is an important component of Drosophila mating systems because it affects sperm usage patterns and sexual selection. Remating is common in females of many species of Drosophila in both natural and laboratory populations. It has been reported in many insect species and also in vertebrates. Female remating is a prerequisite for sperm competition between males, and the consequences of this competition, such as sperm precedence or sperm displacement, have been reported for many species of Drosophila. Female remating is dependent on the amount of sperm stored, the male seminal fluid components, nutrition, the quantity of eggs laid, experimental design and density of flies in laboratory. Remating by a female is an insurance against male sterility and sub-fertility and increases genetic heterogeneity of female offspring. Remating gives greater female productivity in many species of Drosophila. We examined female remating with respect to sperm competition and sexual selection in Drosophila and addressed the possible benefits for females. We also reviewed the role of accessory gland fluid in remating, costs associated with remating, the genetic basis of female remating and some possible mechanisms of sperm competition in the light of last male sperm priority and paternity assurance in Drosophila and other insects. We also suggest future areas of research.