Alternative phenotypes of male mating behaviour in the two-spotted spider mite

Severe intraspecific competition for mates selects for aggressive individuals but may also lead to the evolution of alternative phenotypes that do not act aggressively, yet manage to acquire matings. The two-spotted spider mite, Tetranychus urticae, shows male mate-guarding behaviour and male–male combat for available females. This may provide opportunity for weaker males to avoid fighting by adopting alternative mating behaviour such as sneaker or satellite tactics as observed in other animals. We investigated male precopulatory behaviour in the two-spotted spider mite by means of video-techniques and found three types of male mating behaviour: territorial, sneaker and opportunistic. Territorial and sneaker males associate with female teleiochrysales and spend much time guarding them. Territorial males are easily disturbed by rival males and engage themselves in fights with them. However, sneaker males are not at all disturbed by rival males, never engage in fights and, strikingly, never face attack by territorial males. Opportunistic males wander around in search of females that are in the teleiochrysalis stage but very close to or at emergence. To quickly classify any given mate-guarding male as territorial or sneaker we developed a method based on the instantaneous response of males to disturbance by a live male mounted on top of a brush. We tested this method against the response of the same males to natural disturbance by two or three other males. Because this method proved to be successful, we used it to collect territorial and sneaker males, and subjected them to morphological analysis to assess whether the various behavioural phenotypes are associated with different morphological characters. However, we found no statistical differences between territorial and sneaker males, concerning the length of the first legs, the stylets, the pedipalps or the body. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s10493-013-9673-y) contains supplementary material, which is available to authorized users

UNIFYING ECOLOGICAL AND EVOLUTIONARY DYNAMICS THROUGH EXPERIMENTAL STOCHASTIC DEMOGRAPHY

Ecological and evolutionary dynamics depend upon variation in birth and death rates. Consequently characterizing birth and death rates, and identifying factors that explain variation in these rates, should be the foundation of population and evolutionary ecology. Given the central role of birth and death, it is perhaps surprising that relatively few population biologists apply the most recent demographic approaches to their research. This may be because demography is seen as little more than accounting, and therefore dull, or because stochastic demography is seen as mathematically challenging. It is our belief that ecologists and evolutionary biologists have much to gain through increased mastery of stochastic demography. Its applications could push forward our understanding of eco-evolutionary dynamics in stochastic environments, and the outcome could further the unification of ecology and evolution. In this essay we briefly explain why mastering demographic approaches should be a desirable objective for any evolutionary ecologist. We start by describing some aspects and insights gained through application of demographic methods, before suggesting an area where we believe application could prove insightful

The stochastic demography of two coexisting male morphs.

Abstract. If genetically distinct morphs coexist under a range of natural conditions, they should have equal long-run fitnesses across a wide range of different stochastic environments. In other words, the sequence and frequency of good and bad environments should not substantially impact long-run growth rates. When different morphs have contrasting life histories that vary with environmental conditions, however, it seems improbable that growth rates can be equivalent across a range of stochastic environments without invoking a strong stabilizing mechanism to explain their persistence. As yet, there has been no research characterizing the long-run stochastic growth rate (lambdaS) of different morphs across a wide range of stochastic environments. Assuming density independence, we show that the two genetic male morphs in the bulb mite (Rhizoglyphus robini-fighters, which are able to kill other mites, and benign scramblers-have similar lambdas in different Markovian environments (different simulated random sequences of good and bad habitats). Elasticity analyses revealed that Xs was most sensitive to perturbation of adult survival rate. A slight (biologically and statistically realistic) increase in scrambler adult survival equalized scrambler and fighter X,. The fitness equivalence of the two morphs suggests that stabilizing mechanisms, such as density or frequency dependence, required to maintain their coexistence, are weak. We advocate that stochastic demography can offer a powerful approach to identify and understand the circumstances under which genetic polymorphisms can be maintained in stochastic environments

Towards a general, population-level understanding of eco-evolutionary change

Most population-level studies of eco-evolutionary dynamics assume that evolutionary change occurs in response to ecological change and vice versa. However, a growing number of papers report simultaneous ecological and evolutionary change, suggesting that the eco-evolutionary consequences of environmental change for populations can only be fully understood through the simultaneous analysis of statistics used to describe both ecological and evolutionary dynamics. Here we argue that integral projection models (IPM), and matrix approximations of them, provide a powerful approach to integrate population ecology, life history theory, and evolution. We discuss key questions in population biology that can be examined using these models, the answers to which are essential for a general, population-level understanding of eco-evolutionary change. © 2012 Elsevier Ltd