This is a time of massive global change. What are the consequences for life on this planet? To determine the answers, we need knowledge of the factors that lead to diversification of animals and plants and the resilience of this biodiversity to further change. We investigate broad patterns in the evolution of morphology, function, and behavior. Most of our research is conducted with Hemipterans in the Family Coreidae, the Leaf-Footed Bugs.
Resource allocation tradeoffs: Males in many species use weapons such as horns, antlers, and spurs to compete with other males for access to females. Larger weapons often allow males to win high-quality territories and mating opportunities. However, many of these weapons are costly to produce and maintain, competing for a limited supply of resources within the body. Life history theory predicts tradeoffs in investment among fitness-related traits. Thus, an individual that grows a larger costly weapon should have less to invest in other costly traits, including testes. Through experimentation, we have discovered instances of weapons-testes tradeoffs in the leaf-footed bugs. Interestingly, the extent and form of these tradeoffs appear to be influenced by internal and external factors. This is an active current area of our research program, with more papers to come soon.
Featured papers: Joseph PN, Emberts Z, Sasson DA, & Miller CW (2018). Males that drop a sexually-selected weapon grow larger testes. Evolution. 72: 113–122. DOI: 10.1111/evo.13387. PDF.
Somjee U, Miller CW, Tatarnic NJ, & Simmons LW (2018). Experimental manipulation reveals a trade-off between weapons and testes. Journal of Evolutionary Biology. 31: 57–65. DOI: 10.1111/jeb.13193. PDF.
Functional performance and diversity in the weapons of sexual selection: Most species of animal possess some type of weapon, but the most extreme weapons found in the natural world are those used by males competing over access to females. These astonishing structures have fascinated people for centuries. In fact, the earliest known human paintings depict the horns of buffalo and rhinoceros, the antlers of stags, and the tusks of mastodons. In spite of the interest these structures have attracted, we still do not know why there is such amazing weapon diversity. Why do some species use tusks to fight over females, while others use their legs? Why do even closely-related species often have such striking differences in their weapons? We are fascinated by the striking diversity of weapons in the leaf-footed bugs and their relatives (Superfamily Coreoidea). We hypothesize that fighting style changes as insects move onto new host plants. Fighting style changes should affect selection on elements of weapon shape, leading to morphological evolution and eventually diversification in weapons across the Superfamily. We are thrilled to be working in a state with such great diversity of leaf-footed bugs. Our research also takes us to Panama, Kenya, Swaziland, South Africa, Australia, and Singapore.
Photo: A hind leg of one of our local species, Acanthocephala femorata. Males in this species wrestle on plants such as sunflower, pressing that prominent spine into the abdomen of their opponents. Successful males become territory holders and interact with females visiting the plants. Weapon reconstruction image courtesy of Dr. Josh Yarrow, UF.
Environmental effects on sexual selection: We examine the importance of environmental variability both for the size and shape of sexually-selected traits and for the process of selection itself.
The beautiful plumes of the birds of paradise and the massive antlers of elk are examples of the elegant traits crafted by sexual selection. The size and shape of such ornaments and weapons can be influenced by food quality, the social environment, and genetics. Interestingly, these factors can also determine what ornaments are attractive and which weapons are ideal for winning fights. Using multiple species of coreid bugs, we have discovered that sexually-selected traits can vary in expression over both space and time in the wild. Juvenile diet affects adult expression of male weapons, testes, copulatory courtship behaviors, and mating receptivity. We have found that females change their mating decisions based on their context, and these effects translate into differences in selection on male traits. Also, we have found that some very small males win contests against much larger males when a female is present in the fighting arena, a pattern that is absent when females are not around.
Miller CW & Svensson E (2014). Sexual selection in complex environments. Annual Review of Entomology 59: 427-445. PDF
Gillespie SR, Tudor MS, Moore AJ, & Miller CW (2014). Sexual selection is influenced by both developmental and adult environments. Evolution 68: 3421-3432. PDF
Procter DS, Moore AJ, & Miller CW (2012). The form of sexual selection arising from male-male competition depends on the presence of females in the social environment. Journal of Evolutionary Biology 25: 803-812. PDF
Miller CW & Emlen DJ (2010). Dynamic effects of oviposition site on offspring sexually-selected traits and scaling relationships. Evolutionary Ecology 24(2): 375-390. PDF
The Superfamily Coreoidea: There are more than 3000 species of these insects worldwide, and male hind femurs (a sexually-selected weapon) are impressively diverse in size and shape. Males in many species (but not all) use their hind legs as weapons to wrestle over access to females and territories. Males with larger legs are often more likely to win male-male contests and have greater mating success.
Florida is a haven for coreoid researchers! We have dozens of local species, each with its own unique fighting style and weapon shape.
On the right, two male leaf-footed cactus bugs, Narnia femorata, compete over a territory on a flowering cactus. Males often turn around and wrestle with their hind legs whilst fighting.