Sex Plant Reprod (2011) 24:97–112 103 Fig. 5 The asexual life cycle of V. carteri. Asexual development in males and females is indistinguishable. During embryogenesis, mature asexual reproductive cells (gonidia) undergo a rapid series of 11–12 cleavage divisions, some of which are asymmetric. The larger cells resulting from these unequal divisions will become the gonidia of the next generation, whereas the smaller cells will become part of the somatic cell population. At the end of cleavage, the embryo is inside out with respect to the adult conﬁguration: its gonidia are on the outside, and the ﬂagella of its somatic cells are pointing toward the interior of the sphere. A morphogenetic process called inversion brings the embryo into its adult conﬁguration through Furthermore, unicellular volvocine algae like Chlamydo- monas show a characteristic breaststroke-type swimming motion, which is inappropriate for propelling a multicel- lular spheroidal organism. In multicellular volvocine algae, the effective strokes of both ﬂagella of each cell beat in more or less the same direction to push the organism for- ward (Gerisch 1959; Hoops and Floyd 1983; Hoops 1993; Ueki et al. 2010). This change in beating was accomplished by an evolutionary rotation of the basal bodies, which underlie the ﬂagella and determine their orientations (Fig. 1) (Gerisch 1959; Greuel and Floyd 1985; Kirk 2005). In multicellular volvocine algae, ﬂagellar beating also evolved in such a way that it results in rotation of the spheroid instead of rotation of the cell, because even in the multicellular species, the simple eyespot of each cell, a primitive visual system, is used like radar to scan the environment for light sources. The evolutionary adjustment of ﬂagellar beating direc- tion in colonial and multicellular volvocine species also coincided with the invention of organismal polarity and an anterior–posterior axis, which is deﬁned by the direction of swimming (Fig. 1). The colonial and multicellular algae swim in a posterior-to-anterior direction because their ﬂa- gella beat in an anterior-to-posterior direction. In volvocine a series of cell movements that resemble gastrulation in animal embryos (Kirk et al. 1982). The juveniles expand by the deposition of ECM and then hatch from their parent spheroid during a process called release. The somatic cells of the parent, lacking reproductive cells and thus incapable of further cleavage, undergo senescence and die, while the gonidia of the juvenile spheroids mature. Under standard conditions (Starr 1969), the asexual life cycle takes 48 h. For clarity, only 4 of the *16 gonidia/embryos/descendant spheroids are shown within each parent spheroid. Photomicrographs of asexual males and females are shown in Fig. 6a, b algae with increased organismal complexity, there is also a gradient in cell size along the anterior–posterior axis, with the largest cells at the anterior pole and the smallest at the posterior pole (Kirk 1998; Ueki et al. 2010). The cell-to- cell distances at the anterior pole are also larger than at the posterior pole. In volvocine species with a germ–soma division of labor, the reproductive cells are normally located within the posterior hemisphere. Another sign of organismal polarity is a gradient in eyespot size, with cells at the anterior pole having the largest and most light-sen- sitive eyespots; at the posterior pole, the eyespots are tiny or absent, making the corresponding cells appear to be blind (Ueki et al. 2010). The differences in eyespot size produce a photoresponsive gradient decreasing from the anterior to the posterior pole of the spheroid, with the highest responses at the anterior and no response at the posterior. The differences in cell and eyespot sizes reﬂect functional differences between previously identical cells and thus the evolution of specialization. The transition to differentiated multicellularity also greatly affected reproductive traits. In C. reinhardtii (Figs. 1, 4) and other less-complex volvocine algae like G. pectorale and P. morum (Fig. 1), there is only one cell type. For asexual reproduction, the biﬂagellate cells grow, 123