TEMPERATURE EFFECTS AND GENOTYPE-BY-ENVIRONMENT INTERACTIONS IN HYBRIDS: HALDANE'S RULE IN FLOUR BEETLES

Area of Science:

• Evolutionary Biology
• Genetics
• Speciation

Background:

• Haldane's rule predicts greater hybrid dysfunction in the heterogametic sex (males).
• This rule is thought to arise from divergent adaptation and genotype-by-environment interactions (GEI).
• Environmental factors can influence the expression of hybrid incompatibilities.

Purpose of the Study:

• To investigate how environmental variation, specifically temperature, affects Haldane's rule in flour beetle hybrids.
• To examine genotype-by-environment interactions in the expression of hybrid traits.
• To understand the role of local adaptation in the indirect effects leading to speciation.

Main Methods:

• Interspecific crosses were performed between two populations of *Tribolium castaneum* (Spain, Madagascar) and *T. freemani*.
• Hybrid progenies were reared across different temperature regimes.
• Sex ratios and morphological abnormalities in hybrid males were quantified.

Main Results:

• Higher temperatures led to a more female-biased sex ratio (increased male mortality) in hybrids.
• Elevated temperatures also increased the incidence of morphological abnormalities in hybrid males.
• Significant genotype-by-environment interactions were observed for both hybrid traits in both populations.

Conclusions:

• Environmental temperature is a critical factor in the expression of Haldane's rule and hybrid incompatibilities.
• GEI plays a substantial role in shaping hybrid traits, supporting the link between local adaptation and speciation.
• Findings highlight the indirect pathway through which local adaptation can drive reproductive isolation.