Sexual Dimorphism and Biotic Interactions

Abstract

In the last decade, an increasing number of studies have suggested that males and females of dioecious plants may be differentially affected by competition, herbivory, and parasitism. In dioecious plant species, there is a fundamental sexual difference in patterns of reproductive allocation. Males may allocate more resources to reproduction than females during flowering, but total reproductive allocation is typically greater in females than in males (Chap. 6). These sexual differences in schedules of reproductive allocation have in several species been found to be associated with differences in vegetative phenology, rate of growth, morphology, and chemical composition (Lloyd and Webb 1977; Chaps. 6 and 7), which are characters that are likely to affect competitive ability and interactions with herbivores and parasites (e.g., Crawley 1983;Keddy 1989;Marquis 1992;Dix and Webster 1995).In this chapter, we first briefly discuss why sexual differences in patterns of reproductive allocation may result in differences in growth and physiology, and we formulate a number of questions concerning the relative competitive ability of the two sexes, and sexual differences in the outcome of interactions with herbivores and parasites. We then present and discuss the results of a literature review performed to answer these questions, and we conclude by discussing some demographic and evolutionary consequences of biotic interactions in dioecious plants and by identifying areas in need of further research. Reproductive Allocation and Biotic InteractionsIn several dioecious species, female plants have been shown to allocate more biomass and nutrients to reproduction than male plants given a certain minimum level of fruit production

Vole response to unintentional changes in the chemistry of GM poplars

“…This suggest that the explanation for the changes is more complicated than simple flow-on effects into the secondary metabolism Despite the well-documented high degree of selectivity of bank voles (e.g. Hansson 1985;Danell et al 1991;HjältØn et al 1996;gren et al 1999;Pusenius 2001;Hallgren & HjältØn 2002) and higher concentration of condensed tannins in line SPS33A and (marginally) SPS26 we found no significant difference in vole preference for the GM poplars and the wild-type. Hallgren & HjältØn (2004) found strong indications that condensed tannins have a negative effect of plant palatability to bank voles.…”

Females make tough neighbors: sex-specific competitive effects in seedlings of a dioecious grass

“…Although comparing male and female traits through all the stages of a species' life-history is critical to understanding the ecology and evolution of dioecious species (Lloyd and Webb 1977;Shine 1989), there is little information on the timing of onset of sex-specific differences in non-morphological traits in dioecious plant species (Dawson and Geber 1999;Å gren et al 1999). The primary reason for the lack of knowledge in this area is that determining the gender of sexually immature individuals using morphology only is impossible for most dioecious plant species (Dawson and Geber 1999).…”

Divergence in Defence against Herbivores between Males and Females of Dioecious Plant Species

“…The first review of the empirical studies on the topic of sex-biased herbivory concluded that “males are more likely than females to be preferentially used by herbivores” and suggested that male-biased herbivory was widespread among dioecious species [72]. The authors, however, recognized that sex-biased herbivory was by no means a unanimous finding across all the dioecious species examined to that date, and that the relative susceptibility of each sex to herbivory could be influenced, among other factors, by fluctuations in ecological tradeoffs between functions (rather than evolutionary changes in patterns of allocation), such as phenological changes in resource allocation to reproduction and growth [75, 89].…”