So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

I. the origin of species by means of natural selection

The Strategy of the Genes

Nothing in biology makes sense except in the light of evolution, quipped Theodosius Dobzhansky. The theory of evolution argues that each biological species was not suddenly and independently created but that all life forms are interrelated by virtue of having descended from common ancestors through the accumulation of modifications. Indeed, nothing we know about living organisms would make any sense if they were not so interrelated. And the theory that biological species are descended from common ancestors provides an indispensable heuristic to understand why living organisms are what they are and do what they do.

Nothing in Biology Makes Sense Except in the Light of Evolution

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Systematics And The Origin Of Species

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.

/pdf/female-remating-sperm-competition-and-sexual-selection-in-2a943dknr7.pdf

Female remating, sperm competition and sexual selection in Drosophila.

Background 
The amount and quality of nutrients consumed by organisms have a strong impact on stress resistance, life-history traits and reproduction. The balance between energy acquisition and expenditure is crucial to the survival and reproductive success of animals. The ability of organisms to adjust their development, physiology or behavior in response to environmental conditions, called phenotypic plasticity, is a defining property of life. One of the most familiar and important examples of phenotypic plasticity is the response of stress tolerance and reproduction to changes in developmental nutrition. Larval nutrition may affect a range of different life-history traits as well as responses to environmental stress in adult.


Principal Findings 
Here we investigate the effect of larval nutrition on desiccation, starvation, chill-coma recovery, heat resistance as well as egg to adult viability, egg production and ovariole number in Drosophila ananassae. We raised larvae on either protein rich diet or carbohydrate rich diet. We found that flies consuming protein rich diet have higher desiccation and heat shock resistance whereas flies developed on carbohydrate rich diet have higher starvation and cold resistance. Egg production was higher in females developed on protein rich diet and we also found trade-off between egg production and Egg to adult viability of the flies. Viability was higher in carbohydrate rich diet. However, sex specific viability was found in different nutritional regimes. Higher Egg production might be due to higher ovariole number in females of protein rich diet.


Conclusion 
Thus, Drosophila ananassae adapts different stress tolerance and life-history strategies according to the quality of the available diet, which are correlated with phenotypic adjustment at anatomical and physiological levels.

/pdf/experimental-evidence-for-nutrition-regulated-stress-14k5gf6g3w.pdf

Experimental evidence for nutrition regulated stress resistance in Drosophila ananassae.

Geographical variation in traits related to fitness is often the result of adaptive evolution. Stress resistance traits in Drosophila often show clinal variation, suggesting that selection affects resistance traits either directly or indirectly. Multiple stress resistance traits were investigated in 45 natural populations of Drosophila ananassae collected from all over India. There was significant positive correlation between starvation resistance and lipid content. Significant negative correlations between desiccation and lipid content and between desiccation and heat resistance were also found. Flies from lower latitudes had higher starvation resistance, heat resistance and lipid content but the pattern was reversed for desiccation resistance. These results suggest that flies from different localities varied in their susceptibility to starvation because of difference in their propensity to store body lipid. Multiple regression analysis provided evidence of climatic selection driven by latitudinal variation in the seasonal amplitude of temperature and humidity changes within the Indian. Finally, our results suggest a high degree of variation in stress resistance at the population level in D. ananassae.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1420-9101.2010.02061.x

Resistance to environmental stress in Drosophila ananassae: latitudinal variation and adaptation among populations

Drosophila ananassae is a cosmopolitan and domestic species. It occupies a nuique status among the Drosophila species due to certain peculiarities in its genetic behaviour. The most unusual feature of this species is spontaneous male recombination in appreciable frequency. The present review summarises the work done on population and behaviour genetics of D. ananassae from India. Population dynamics of three cosmopolitan inversions has been studied in Indian population of D. ananassae and it is evident from the results that there is a considerable degree of genetic divergence at the level of inversion polymorphism. In general, the populations from south India show more differentiation than those from the north. These three cosmopolitan inversions, which are coextensive with the species, exhibit heterosis. Interracial hybridization does not lead to beaakdown of heterosis, which suggests that evidence for coadaptation is lacking in geographic populations of D. ananassae. Heterosis appears to be simple luxuriance rather than populational heterosis (coadaptation). Unlinked inversions occur in random associations, indicating no interchromosomal interactions. However, two inversions of the third chromosome often show strong linkage disequilibrium in laboratory populations, which is due to epistatic gene interaction and suppression of crossing-over. Genetic variations for certain allozyme polymorphism and sternoleural bristle phenotypes in Indian populations of D. ananassae have also been observed.

Population and behaviour genetics of Drosophila ananassae.

Female remating is the fundamental to evolutionary biology, as it determines the pattern of sexual selection and sexual conflict. During the course of the present study, female remating behaviour of six species of Drosophila, D. ananassae, D. nasuta, D. eugracilis, D. melanogaster, D. simulans and D. pseudoananassae was observed and compared. Periodic confinement design (2 h daily observation) was used for female remating experiments. The frequency of female remating ranges from 16 (D. eugracilis) to 82% (D. melanogaster) in different species of Drosophila, and the differences among different species are statistically significant. Remating latency also varies from 5.51 days (D. melanogaster) to 9.85 days (D. pseudoananassae) in different species, and variation among different species is statistically significant. Duration of copulation in first (virgin mating) and second (remating) matings was observed and compared in each of the six species. Among all the species tested, females of D. ananassae, D. nasuta, D. eugracilis, and D. pseudoananassae show significantly shorter duration of copulation in the second mating compared to the first mating, while D. simulans females show shorter duration of copulation in the second mating compared to the first mating, but the difference is statistically not significant. However, D. melanogaster females show significantly longer duration of copulation in the second mating compared to first mating. Based on these findings, it may be suggested that different species of Drosophila may vary in the incidence of remating and duration of copulation due to differences in their reproductive biology and adaptation.

Bashisth N. Singh

Papers

Female remating, sperm competition and sexual selection in Drosophila.

Experimental evidence for nutrition regulated stress resistance in Drosophila ananassae.

Resistance to environmental stress in Drosophila ananassae: latitudinal variation and adaptation among populations

Population and behaviour genetics of Drosophila ananassae.

Female remating in Drosophila: Comparison of duration of copulation between first and second matings in six species