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Developmental plasticity, the ability of individuals to adjust their phenotypes in response to variable environmental conditions, is widespread across taxa. Most organisms exhibit plasticity in one or more traits and in response to one or more environmental factors. Yet, how do organisms integrate environmental information and develop a phenotypic response?
Our research focuses on polyphenisms, an extreme form of plasticity characterized by alternative morphologies. Specifically, we use two systems Onthophagus horned beetles and Pristionchus predatory nematodes. We use a combination of functional genetics (RNAi, CRISPR/Cas9), genomics, transcriptomics and behavioral assays to address diverse questions taking an integrative approach. Mechanisms and evolution of morphological plasticity Onthophagus horned beetles are a model system for studying the intersection of ecology with evolutionary developmental biology. Male beetles exhibit an extreme form of developmental plasticity, polyphenism. Low nutrition males develop as small, hornless individuals, whereas high nutrition males develop as large, horned individuals. The genus Onthophagus is incredibly diverse and species differ in the degree of horn plasticity. Some species exhibit exaggerated horn growth and plasticity, whereas others exhibit a more moderate response, and yet other species have completely lost plasticity and horn growth. Our research using horned beetles seeks to understand what are the genetic and genomic mechanisms regulating plastic horn development and their evolution? Regulation of sexual dimorphism and its evolution The nematode Pristionchus pacificus is a model for developmental plasticity. Species in the family Diplogastridae are characterized by a mouth polyphenism in response to starvation and crowding. Under low food availability and crowding, individuals develop a wide mouth morphology (“eurystomatous”, "Eu"), that prey on other nematodes. In contrast, under high food availability and low population densities individuals develop a narrow-mouth morphology (“stenostomoatous”, "St") that feeds on bacteria and develops faster than their predatory counterpart. Pristionchus nematodes are also known to be diverse in reproductive mode (male and female vs. hermaphrodites) and sexual dimorphism. Some species exhibit polyphenism mostly in females or hermaphrodites, whereas others display polyphenism in both sexes. Our research using predatory nematodes seeks to understand how is the sexual dimorphism regulated and how do these mechanisms evolve? Regulation and evolution of behavioral plasticity in alternative phenotypes Male Onthophagus beetles exhibit a nutritional polyphenism characterized by exaggerated horn growth in large, high nutrition males and reduced horn growth in small, low nutrition males. Horns in large males are used as weapons to gain access to females. Hornless males instead use a sneaker tactic, bypassing large males to gain access to females. Our research seeks to understand what are the mechanisms regulating behavioral plasticity, how are they integrated with morphological plasticity, and how do they evolve? The nematode Pristionchus pacificus develops a predatory morphology (“Eu”) in response to crowding and starvation. Instead, low population densities and high food availability result in a microbivore morphology (“St”). We use this system to ask: what are the mechanisms that regulate predatory and microbivore behaviors, how are they integrated with morphology, and how do they evolve? |
Diversity of horn plasticity across species. Small, low nutrition males (left) are hornless, whereas large, high nutrition males (right) are horned.
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Pristionchus pacificus polyphenism. Stenostomatous (St), microbivore morph (A) and eurystomatous (Eu), predatory morph (B). (C) The Eu morph can prey on other nematodes.
