Commentary on the chastity of amoebae: re-evaluating evidence for sex in amoeboid organisms.

A student in one of my mycology classes, after she had Though there are lots of ways cells and, ultimately, their been exposed to numerous life cycles, commented, ‘All you mycologists ever think about is sex.’ In a way, it is too bad that biologists, in general, do not spend enough time thinking critically about sex as a biological phenomenon. Lahr et al. [1], in their review of sex in amoeboid eukaryotes, make a good start at calling attention to this problem. It is amazing how little we teach young, potential biologists about the true generalities of biology. If one examines any basic biology text, one comes away with the impression that animals, particularly vertebrates, are the exemplars for all living things. Thus, too many examples are drawn from animals and too few are drawn from the range of variations that are present among the eukaryotes as a whole. That is, students are poorly introduced to the comparative method in biology, and when they become practising biologists, they often cannot put important biological processes in a proper context. Sex is one area where biologists are not well trained. Many biologists have probably never been asked to state succinctly what is universal about sex, so they have a hard time recognizing its universal features. It is a phenomenon that is exclusive to eukaryotes. Lahr et al. [1] elegantly define the essential components of sex; they are ‘ . . . the presence of a meiotic reduction of the genome complement followed eventually by karyogamy . . . in an organism’s life cycle.’ Thus, we see that sex is, at its heart, a nuclear phenomenon where there is a stereotypical mechanism for alternating between diploidy and haploidy. Sex is not reproductive, though it is often linked with reproduction as it is in most animals. Therefore, animals are poor models for understanding the universal aspects of sex. The definition of reproduction should be limited to the production of a greater number of individuals from a smaller number of individuals. Fertilization, at least when gametic cells are involved, results in a reduction in the number of individuals from two cells to one, a zygote. I will grant that meiosis can potentially be reproductive if all four potential nuclei become housed in individual cells, but that is hardly the rule. At best, one could make a case for sexual reproduction only if one found a hypothetical (and never reported) sexual life cycle where mitosis and somatic growth do not occur and the meiotic nuclei were housed in four cells. In such a case, there would be a net gain of two haploid cells per life cycle (2 cells !1 cell ! 4 cells ! 2 cells ! 8 cells . . . ). Without such an organism, there is no point in using the term sexual reproduction.