N. V. Joshi
Articles written in Journal of Genetics
Volume 64 Issue 1 July 1985 pp 41-58
A model is constructed to study the effects of local mate competition and multiple mating on the optimum allocation of resources between the male and female reproductive brood in social hymenopteran colonies from the ‘points of view’ of the queen (parental manipulation theory) as well as the workers (kin selection theory). Competition between pairs of alleles specifying different sex investment ratios is investigated in a game theoretic frame work. All other things being equal, local mate competition shifts the sex allocation ratio in favour of females both under queen and worker control. While multiple mating has no effect on the queen’s optimum investment ratio, it leads to a relatively male biased investment ratio under worker control. Under queen control a true Evolutionarily Stable Strategy
Volume 66 Issue 1 April 1987 pp 69-84
The iterative two-person Prisoners’ Dilemma game has been generalised to the
The hardest TFT can go to fixation against the selfish strategy provided it crosses a threshold frequency
Volume 67 Issue 3 December 1988 pp 161-171
When there is a variation in the quality of males in a population, multiple mating can lead to an increase in the genetic fitness of a female by reducing the variance of the progeny number. The extent of selective advantage obtainable by this process is investigated for a population subdivided into structured demes. It is seen that for a wide range of model parameters (deme size, distribution of male quality, local resource level), multiple mating leads to a considerable increase in the fitness. Frequency-dependent selection or a stable coexistence between polyandry and monandry can also result when the possible costs involved in multiple mating are taken into account.
Volume 69 Issue 3 December 1990 pp 127-139
For a population made up of individuals capable of sexual as well as asexual modes of reproduction, conditions for the spread of a transposable element are explored using a one-locus, two-haplotype model. The analysis is then extended to include the possibility that the transposable element can modulate the probability of sexual reproduction, thus casting Hickey’s (1982,
Volume 70 Issue 2 August 1991 pp 103-127
Polyembryony, referring here to situations where a nucellar embryo is formed along with the zygotic embryo, has different consequences for the fitness of the maternal parent and offspring. We have developed genetic and inclusive fitness models to derive the conditions that permit the evolution of polyembryony under maternal and offspring control. We have also derived expressions for the optimal allocation (evolutionarily stable strategy, ESS) of resources between zygotic and nucellar embryos.
It is seen that (i) Polyembryony can evolve more easily under maternal control than under that of either the offspring or the ‘selfish’ endosperm. Under maternal regulation, evolution of polyembryony can occur for any clutch size. Under offspring control polyembryony is more likely to evolve for high clutch sizes, and is unlikely for low clutch sizes (<3). This conflict between mother and offspring decreases with increase in clutch size and favours the evolution of polyembryony at high clutch sizes, (ii) Polyembryony can evolve for values of “
Finally we argue that polyembryony is a maternal counter strategy to compensate for the loss in her fitness due to brood reduction caused by sibling rivalry. We support this assertion by two empirical evidences: (a) the extent of polyembryony is positively correlated with brood reduction in
Volume 70 Issue 2 August 1991 pp 135-135 Erratum
Volume 71 Issue 3 December 1992 pp 105-119
Competition between seeds within a fruit for parental resources is described using one-locus-two-allele models. While a “normal” allele leads to an equitable distribution of resources between seeds (a situation which also corresponds to the parental optimum), the “selfish” allele is assumed to cause the seed carrying it to usurp a higher proportion of the resources. The outcome of competition between “selfish” alleles is also assumed to lead to an asymmetric distribution of resources, the “winner” being chosen randomly. Conditions for the spread of an initially rare selfish allele and the optimal resource allocation corresponding to the evolutionarily stable strategy, derived for species with n-seeded fruits, are in accordance with expectations based on Hamilton’s inclusive fitness criteria. Competition between seeds is seen to be most intense when there are only two seeds, and decreases with increasing number of seeds, suggesting that two-seeded fruits would be rarer than one-seeded or many-seeded ones. Available data from a large number of plant species are consistent with this prediction of the model.
Volume 72 Issue 2-3 December 1993 pp 47-58
Any statement on the optimality of the existing code ought to imply that this code is ideal for conserving a certain hierarchy of properties while implying that other codes may have been better suited for conservation of other hierarchies of properties. We have evaluated the capability of mutations in the genetic code to convert one amino acid into another in relation to the consequent changes in physical properties of those amino acids. A rather surprising result emerging from this analysis is that the genetic code conserves long-range interactions among amino acids and not their short-range stereochemical attributes. This observation, based directly on the genetic code itself and the physical properties of the 20 amino acids, lends credibility to the idea that the genetic code has not originated by a frozen accident (the null hypothesis rejected by these studies) nor are stereochemical attributes particularly useful in our understanding of what makes the genetic code ‘tick’. While the argument that replacement of, say, an aspartate by a glutamate is less damaging than replacement by arginine makes sense, in order to subject such statements to rigorous statistical tests it is essential to define what constitutes a random sample for the genetic code. The present investigation describes one possible specification. In addition to obvious statistical considerations of testing hypotheses, this procedure points to the more exciting notion that alternative codes may have existed.
Volume 74 Issue 1-2 April 1995 pp 77-83 Book Review
Volume 77 Issue 2-3 August 1998 pp 133-134 Software Review
Volume 79 Issue 1 April 2000 pp 9-15
The very insightful Trivers-Willard hypothesis, proposed in the early 1970s, states that females in good physiological condition are more likely to produce male offspring when the variance of reproductive success among males is high. The hypothesis has inspired a number of studies over the last three decades aimed at its experimental verification, and many of them have found adequate supportive evidence in its favour. Theoretical investigations, on the other hand, have been few, perhaps because formulating a population-genetic model for describing the Trivers-Willard hypothesis turns out to be surprisingly complex. The present study is aimed at using a minimal population-genetic model to explore one specific scenario, namely how is the preference for a male offspring by females in good condition altered when
Volume 79 Issue 3 December 2000 pp 133-134 Book Review
Volume 81 Issue 2 August 2002 pp 87-89 Book Review
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