CLINAL PATTERNS OF CHROMOSOMAL INVERSION POLYMORPHISMS INDROSOPHILA SUBOBSCURAARE PARTLY ASSOCIATED WITH THERMAL PREFERENCES AND HEAT STRESS RESISTANCE

Abstract

Latitudinal clines in the frequency of various chromosomal inversions are well documented in Drosophila subobscura. Because these clines are roughly parallel on three continents, they have undoubtedly evolved by natural selection. Here, we address whether individuals carrying different chromosomal arrangements also vary in their thermal preferences (T p ) and heat stress tolerance (T ko ). Our results show that although T p and T ko were uncorrelated, flies carrying "cold-adapted" gene arrangements tended to choose lower temperatures in the laboratory or had a lower heat stress tolerance, in line with what could be expected from the natural patterns. Different chromosomes were mainly responsible for the underlying genetic variation in both traits, which explains why they are linearly independent. Assuming T p corresponds closely with temperatures that maximize fitness our results are consistent with previous laboratory natural selection experiments showing that thermal optimum diverged among thermal lines, and that chromosomes correlated with T p differences responded to selection as predicted here. Also consistent with data from the regular tracking of the inversion polymorphism since the colonization of the Americas by D. subobscura, we tentatively conclude that selection on tolerance to thermal extremes is more important in the evolution and dynamics of clinal patterns than the relatively "minor" adjustments from behavioral thermoregulation.

Extreme cost of rivalry in a monandrous species: male–male interactions result in failure to acquire mates and reduced longevity

“…The data are notable because D. subobscura is commonly used as a model of stress tolerance in nature [41][42][43]. However, stress tolerance studies in this species have focused on thermal effects on genetic and phenotypic polymorphisms of wings and desiccation resistance [43 -45].…”

Evolutionary capacity of upper thermal limits: beyond single trait assessments

“…Previous work (Sgrò et al, 2010) has shown that all three measures of heat tolerance show parallel clines in D. melanogaster populations from along the east coast of Australia that reflect the action of selection and not neutral processes. Furthermore, we know that temperature is a significant selective agent for Drosophila (Huey and Pascual, 2009;Kellermann et al, 2012;Rego et al, 2010), and the observed clinal patterns in heat tolerance in D. melanogaster (Sgrò et al, 2010) reflect this. However, whether these parallel clinal patterns are the result of independent selection acting on all three measures of heat tolerance or reflect a shared genetic basis remains unknown.…”

“…Importantly, behavioural thermoregulation may have a limited ability to ameliorate the effects of climate warming in ectotherms (Huey and Pascual, 2009;Kearney et al, 2009;Rego et al, 2010), and temperature is expected to impose significant selection pressures on both ectotherms and endotherms (e.g. Huey et al, 2012).…”

Medium-term changes in Drosophila subobscura chromosomal inversion polymorphism: a possible relation with global warming?

“…Finally for the O chromosome, O st ('cold') frequency slightly increased (P = 1), and among the 'warm' adapted, O 3+4 decreased (P = 0.755), whereas O 3+4+1 (P = 1) and O 3+4+8 (P = 0.527) increased. Following Rego et al (2010), we have tested whether there were differences between 'cold' and 'warm' groups of inversions in this seven year period. Analysing all chromosomes together or individually, in both conditions no significant variation was seen (P = 0.520, when analysing all chromosomes) and individually: A (P = 1), J (P = 1), E (P = 1), O (P = 1) and U (P = 0.082).…”