@article {1563,
	title = {Integrating development with evolution: a case study with beetle horns},
	journal = {Bioscience},
	volume = {50},
	number = {5},
	year = {2000},
	month = {May},
	pages = {403-418},
	author = {Emlen, Douglas J.}
}
@article {1569,
	title = {The development and evolution of exaggerated morphologies in insects},
	journal = {Annual Review of Entomology},
	volume = {45},
	year = {2000},
	pages = {661-708},
	abstract = {We discuss a framework for studying the evolution of morphology in insects, based on the concepts of {\textquoteleft}{\textquoteleft}phenotypic plasticity{\textquoteright}{\textquoteright} and {\textquoteleft}{\textquoteleft}reaction norms.{\textquoteright}{\textquoteright} We illustrate this approach with the evolution of some of the most extreme morphologies in insects: exaggerated, sexually selected male ornaments and weapons, and elaborate social insect soldier castes. Most of these traits scale with body size, and these scaling relationships are often nonlinear. We argue that scaling relationships are best viewed as reaction norms, and that the evolution of exaggerated morphological traits results from genetic changes in the slope and/or shape of these scaling relationships. After reviewing literature on sexually selected and caste-specific structures, we suggest two possible routes to the evolution of exaggerated trait dimensions: (a) the evolution of steeper scaling relationship slopes and (b) the evolution of sigmoid or discontinuous scaling relationship shapes. We discuss evolutionary implications of these two routes to exaggeration and suggest why so many of the most exaggerated insect structures scale nonlinearly with body size. Finally, we review literature on insect development to provide a comprehensive picture of how scaling relationships arise and to suggest how they may be modified through evolution.},
	keywords = {allometry, castes, Polyphenism, sexual selection, threshold traits},
	author = {Emlen, Douglas J. and Nijhout, H. Frederik}
}
@article {2034,
	title = {Male horn dimorphism in the scarab beetle, Onthophagus taurus: do alternative reproductive tactics favour alternative phenotypes},
	journal = {Animal Behavior},
	volume = {59},
	year = {2000},
	pages = {459-466},
	abstract = {In a variety of organisms morphological variation is discrete rather than continuous. Discrete variation within a sex has attracted particular interest as it is thought to reflect the existence of alternative adaptations to a heterogeneous selection environment. The beetle Onthophagus taurus shows a dimor- phism for male horns: males that exceed a critical body size develop a pair of long, curved horns on their heads, while smaller males remain hornless. In this study we report on the alternative reproductive tactics used by males with these two morphologies, and present experimental and behavioural data suggesting that these alternative tactics selectively favour discretely different male phenotypes. Horned males aggressively defended tunnel entrances containing breeding females. Fights involved the use of horns, and males with longer horns were more likely to win fights. In contrast, hornless males employed nonaggressive sneaking behaviours when faced with competitively superior males. Sneaking behaviours appeared to require high degrees of manoeuvrability inside tunnels to access and mate with females despite the presence of a guarding male. Comparisons of running performances of males with identical body sizes but different horn lengths suggest that the possession of horns reduces male agility inside tunnels. Thus, horn possession confers a clear advantage to males using fighting behaviours to access females, whereas hornlessness may be favoured in males that rely primarily on sneaking behaviours. Combined, the two alternative reproductive tactics used by male O. taurus appear to favour opposite horn phenotypes, which may explain the paucity of intermediate morphologies in natural populations of O. taurus. },
	author = {Moczek, Armin P. and Emlen, Douglas J.}
}
