Haldane and modern evolutionary genetics

Physiological aspects of sex differences and Haldane's rule in Rumex hastatulus

Haldane's rule (HR, impairment of fertility and/or viability of interracial hybrids) seems to be one of few generalizations in evolutionary biology. The validity of HR has been confirmed in animals, and more recently in some dioecious plants (Silene and Rumex). Dioecious Rumex hastatulus has two races differing in the sex chromosome system: Texas (T) and North Carolina (NC), and T × NC males showed both reduced pollen fertility and rarity-two classical symptoms of Haldane's rule (HR). The reduced fertility of these plants has a simple mechanistic explanation, but the reason for their rarity was not elucidated. Here, we measured selected physiological parameters related to the antioxidant defense system in parental races and reciprocal hybrids of R. hastatulus. We showed that the X-autosome configurations, as well as asymmetries associated with Y chromosomes and cytoplasm, could modulate this system in hybrids. The levels and quantitative patterns of the measured parameters distinguish the T × NC hybrid from the other analyzed forms. Our observations suggest that the rarity of T × NC males is caused postzygotically and most likely related to the higher level of oxidative stress induced by the chromosomal incompatibilities. It is the first report on the physiological aspects of HR in plants.

Quantifying maladaptation during the evolution of sexual dimorphism

Females and males have distinct trait optima, resulting in selection for sexual dimorphism. However, most traits have strong cross-sex genetic correlations, which constrain evolutionary divergence between the sexes and lead to protracted periods of maladaptation during the evolution of sexual dimorphism. While such constraints are thought to be costly in terms of individual and population fitness, it remains unclear how severe such costs are likely to be. Building upon classical models for the 'cost of selection' in changing environments (sensu Haldane), we derived a theoretical expression for the analogous cost of evolving sexual dimorphism; this cost is a simple function of genetic (co)variances of female and male traits and sex differences in trait optima. We then conducted a comprehensive literature search, compiled quantitative genetic data from a diverse set of traits and populations, and used them to quantify costs of sexual dimorphism in the light of our model. For roughly 90% of traits, costs of sexual dimorphism appear to be modest, and comparable to the costs of fixing one or a few beneficial substitutions. For the remaining traits (approx. 10%), sexual dimorphism appears to carry a substantial cost-potentially orders of magnitude greater than costs of selection during adaptation to environmental changes.

J. B. S. Haldane and Journal of Genetics

This is a brief sketch of the history of Journal of Genetics from its beginning in 1909 to the taking over of its publication by the Indian Academy of Sciences in 1985. The account is centred on J. B. S. Haldane's involvement with it over many years, especially as Editor, initially in the UK and later in India.