Abstract
About eight million animal species are estimated to live on Earth, and all except those belonging to one subphylum are invertebrates. Invertebrates are incredibly diverse in their morphologies, life histories, and in the range of the ecological niches that they occupy. A great variety of modes of reproduction and sex determination systems is also observed among them, and their mosaic-distribution across the phylogeny shows that transitions between them occur frequently and rapidly. Genetic conflict in its various forms is a long-standing theory to explain what drives those evolutionary transitions. Here, we review (1) the different modes of reproduction among invertebrate species, highlighting sexual reproduction as the probable ancestral state; (2) the paradoxical diversity of sex determination systems; (3) the different types of genetic conflicts that could drive the evolution of such different systems.
Highlights
About eight million animal species are estimated to live on Earth, and all except those belonging to one subphylum are invertebrates
The two kinds of gametes required for sexual reproduction are produced through meiosis, (1) allowing for recombination of the parental genomes to produce new combinations of genetic material, which is thought to underlie the success of sex in eukaryotes [6]; (2) reducing the diploid genome to a haploid set, with diploidy being restored through the fusion of gametes after fertilization
The existence of these various reproductive modes raises important questions, such as: if sex facilitates adaptation, why do so many lineages reproduce asexually? Do the mechanisms underlying asexual reproduction matter to their evolutionary dynamics? If hermaphrodites have the benefits of sex at a lower cost, why are species with separate sexes so widespread? we discuss the distribution of reproductive modes among invertebrate species, and its implications for some of these questions
Summary
Reproduction consists of the vertical transmission of genetic material from parent(s) to the generation. The two kinds of gametes required for sexual reproduction are produced through meiosis, (1) allowing for recombination of the parental genomes to produce new combinations of genetic material, which is thought to underlie the success of sex in eukaryotes [6]; (2) reducing the diploid genome to a haploid set, with diploidy being restored through the fusion of gametes after fertilization. Male and female gametes can be produced by the same individual (simultaneously or successively) in hermaphroditic species, or by two separate sexes in gonochoric species. The existence of these various reproductive modes raises important questions, such as: if sex facilitates adaptation, why do so many lineages reproduce asexually? The existence of these various reproductive modes raises important questions, such as: if sex facilitates adaptation, why do so many lineages reproduce asexually? Do the mechanisms underlying asexual reproduction matter to their evolutionary dynamics? If hermaphrodites have the benefits of sex at a lower cost (such as the need to find a mate of the opposite sex), why are species with separate sexes so widespread? we discuss the distribution of reproductive modes among invertebrate species, and its implications for some of these questions
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