Evolution and Speciation in Animals

This book represents the first attempt to quantify environmental factors and life history traits that accelerate or decelerate species diversity in animals. About 15%, 8% and 77% of species are distributed in marine (70% of earth’s surface), freshwater (< 1%) and terrestrial (~ 29%) habitats. Hence, the terra firma fosters more diversity. The harsh hadal, desert and elevated montane habitats restrict diversity to 0.5-4.2%. Costing more time and energy, osmotrophic and suspension modes of food acquisition limit diversity to < 20%. In minor phyletics, evolution has proceeded from a ‘wrong combination’ of low motility and gonochorism to sessility and hermaphroditism. The motile major phyletics are more speciose (166,279 species/phylum) than the latter (1,975 species/phylum). As evolution and speciation are driven by motility, sessility is limited to 2.9% animals. Selfing hermaphrodites (0.9%), parthenogens (< 0.6%) and clonals (~ 2%) miss meiosis and/or fertilization. Unable to tolerate them together, animals mutually eliminate parthenogenesis and hermaphroditism as well as parthenogenesis and cloning from each other. In clonals, colonial budding (94%) is more common than costlier fragmentation in solitary clonals. The newly proposed hypothesis explains that each stem cell plays an additive role and the required mass of stem cells differs for cloning and regeneration. Incidence of heterogamety is four-times more in males than in females. Hence, evolution is more a male-driven process. Egg size is determined by environmental factors, but lecithality is genetically fixed. In poikilotherms, sex is also determined by gene(s), but differentiation by environmental factors. The extra-ovarian vitellogenesis (> 96%), spermatozoan (81%) rather than spermatophore mechanism of sperm transfer, promiscuity and polygamy over monogamy, iteroparity (99.6%) over semelparity and internal fertilization (84%) are preferred, as they accelerate diversity. Body size and egg size determine fec