Alternative reproductive tactics associated with variable sensory biology and thermal physiology in male Centris pallida (Hymenoptera: Apidae) bees

Meghan Barrett

doi:10.17918/00001166

Climate change is predicted to cause significant increases in global temperatures that will place many species under temperature-dependent selection. The consequences of climate change may be especially severe for ectothermic species, which rely heavily on their environment to maintain a non-lethal body temperature. Little attention has been paid to the potential effects of climate change on variable morphology, physiology, or behavior within a species. Alternative reproductive tactics (ARTs) occur when there is categorical variation in the mating-related behavior or morphology of individuals of one sex within a population, and are ideal for investigating the impacts of the thermal environment on behavioral, physiological, or morphological variation. Males of the Sonoran Desert bee Centris pallida use ARTs and are dimorphic in both behavior and morphology. Large-morph males use a fixed strategy that relies on scent to locate mates buried underground. Small-morph males are behaviorally flexible, generally using visual cues to locate females in the sky but sometimes using the scent-based strategy. First, I characterized variation in neuroanatomy between large and small morph C. pallida males, demonstrating that relative investment in visual and olfactory peripheral processing regions support the different mate-location tactics used by the morphs. Next, I demonstrated that small-morph males have increased relative investment in eye size and ommatidia density, but reduced total ommatidia numbers, eye surface areas, and visual acuities compared to large males. These data suggest that both allometric constraints associated with body size and mate location behaviors correlate with external visual investment. Finally, I investigated physiology and morphological adaptations to the microclimates used by the morphs: large-morph males use a hotter microclimate near the ground while small-morph males hover several feet above the surface. Small-morph males have increased thermal tolerance compared to large-morph males, despite a cooler microclimate, suggesting they use a physiological thermal adaptation to survive high environmental temperatures. Large-morph males have increased reflectance of solar radiation on their dorsal, but not ventral, surface as compared to small-morph males, representing a morphological thermal adaptation to the high solar radiation and ambient temperatures experienced in their microclimate. Together, these data suggest that individuals within a species may vary significantly in their adaptive potential under climate change. Variation in morphological/neuroanatomical systems may support different behaviors for individuals within the same species, sex, and population. Unique thermal adaptations, physiological or morphological, may cause differentiation in the intraspecific selective effects of climate change with important implications for range shifts, intraspecific behavioral diversity, and species' survival.

Alternative reproductive tactics associated with variable sensory biology and thermal physiology in male Centris pallida (Hymenoptera: Apidae) bees

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Alternative reproductive tactics associated with variable sensory biology and thermal physiology in male Centris pallida (Hymenoptera: Apidae) bees

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