Reproductive manipulators

Wolbachia endosymbionts are abundant in arthropods, where they promote a variety of reproductive manipulations, including feminization of genetic males, parthenogenesis and cytoplasmic incompatibility. Wolbachia is also present in filarial nematodes and has recently attracted a great deal of attention. This chapter reviews the studies so far published and discusses potential implications and future research prospects. Since this is a relatively young field, the chapter will also refer to unpublished studies and will include some speculation. The aim is to stimulate further work on the subject. 

Von Neumann s machine is actually an example of a universal constructor. It must not only carry out logical operations (i.e. act as a universal computer), but must also be able to identify and manipulate various components. The universal constructor C must be able to both (1) construct the machine whose blueprint appears in symbolic form on its input tape and (2) attach a copy of that same blueprint to the machine once it is constructed. Self-reproduction is the special case where C s input tape actually contains the blueprint data for C itself. Alas, there are a few subtleties. 

The consistency of the effects noted above and in Chap. 5 which modulate reproduction and involve the operation of the AOS, are unlikely to be wholly artifacts of captivity. Nevertheless, it needs to be shown which of the influences on male and female fertility have relevance to natural populations (Fig. 7.12). As mentioned, very few experiments on free-living social mammals have been reported, since the logistical problems of stimulus manipulation and control are formidable. A semi-feral population is an acceptable substitute, and provides some means of testing assumptions on the relevance of findings on caged laboratory-bred rodents. 

Manipulation of each of these equations4 yields the condition for expanded reproduction... 

In rabbits, Oryctolagus cuniculus, urine of an adult female delays growth and sexual development in unrelated young males, while mother s urine also delays body growth, but it accelerates sexual development in her own sons. This can he seen as females manipulating the reproductive success of nearby conspecifics (Bell, 1986). 

Depending upon the circumstance and desired effects, endocrine-disrupting chemicals can be either good or bad. The endocrine system is a finely balanced system responsible for fertility and many of the feminine and masculine traits we are all familiar with. Endocrine disruptors are used by millions of women in the form of the pill to control fertility. Chemicals in birth control pills subtly manipulate the endocrine system to reduce fertility. Unfortunately, we now know that many chemicals are capable of influencing the endocrine systems. When these chemicals, such as DDT and TCDD, are released into the environment, they reduce the fertility of wildlife. Exposure to endocrine disruptors is linked to decreased fertility in shellfish, fish, birds, and mammals. Endocrine disruptors such as nonylphenol have been shown to feminize male fish, interfering with reproduction. Some studies have also linked exposure to endocrine disruptors to decreases in human male sperm count. Ironically, urinary metabolites of the birth control pill as well as the female hormone estrogen pass through waste treatment plants and are released into the aquatic environment, where even small concentrations cause feminization of male fish. 

Despite their reproductive potential, workers do not normally activate their ovaries in the presence of the established reproductives. Early observations already indicated the involvement of pheromones in the lack of worker reproduction (Fletcher and Ross, 1985 Holldobler and Bartz, 1985). These pheromones most likely do not directly act on the reproductive physiology of workers, which would be a type of parental manipulation. They are more likely signals that indicate the presence of a healthy and fertile queen to the workforce (Seeley, 1985 Keller and Nonacs, 1993). Workers benefit in this situation from raising offspring rather than from their own reproduction. Nevertheless some workers may activate their ovaries, which is not in the interest of other colony members (Bourke and Franks, 1995). Kin selection theory predicts that either the principal reproductive or other workers should prevent their reproduction (Ratnieks, 1988 Ratnieks et al, 2006). A necessary requirement for this interference is that incipient subordinate egg-layers or their eggs are identified. 

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