Evolution of Fast Development of Planktonic Embryos to Early Swimming

Abstract

Planktonic embryos of marine animals swim at an early stage and age. Although natural selection has apparently favored rapid development of structures for swimming, taxa have not converged on the same, minimal time from first cell division to first swimming. Comparisons of 34 species with planktonic embryos in 10 phyla revealed factors that account for variation in time to swimming. Time to first swimming correlated significantly with time from first to second cleavage (first cell cycle) in analyses of all embryos sampled and separately within the Spiralia and Echinodermata. Time to first swimming also correlated significantly with egg diameter in some clades, but not in all. Correlations between egg diameter and cell cycle duration were low except for the three species of Urochordata. Development to a feeding or nonfeeding larva did not affect time to first swimming beyond effects attributable to egg size. Time to first swimming did not correlate with type of locomotion developed (uniciliated cells, multiciliated cells, or muscle). Nonetheless, differences in locomotion are associated with changes in cell cycle durations prior to swimming. The ratios of time to first swimming and time for first cell cycle suggests that allocation of time to multiplication of cells versus differentiation of cells is resolved differently in species with different types of locomotion.

Unshelled abalone and corrupted urchins: development of marine calcifiers in a changing ocean

“…Owing to the interdependence between temperature, mineral saturation state and pH, the mechanism of this facilitation is likely to be complex. The increase in development rate and calcification in H. erythrogramma and T. gratilla with increased temperature (þ28C) is typical of echinoderm development [50]. However, the decrease in the percentage of normal juveniles at 20 -228C and pH 7.6 -7.8, and the more extreme treatments projected by 2100 (approx.…”

“…Despite the well-known controlling influence of temperature on marine invertebrate development [36,50], recent studies on impacts of climate change on life histories have focused on ocean acidification as a single stressor (reviews in [5 -7,13]). Marine propagules of shallow-water species, however, are experiencing simultaneous warming and acidification from the outset of development.…”

Larval size and age affect colonization in a marine invertebrate

“…However, clearly, smaller larvae can react sooner than larger larvae to cues for high-quality habitat. The reasons for smaller offspring being able to react to cues sooner are unclear, but interspecific comparisons on marine invertebrates show that species with larger eggs tend to have slower initial cell-cycle durations than species with smaller eggs (Staver and Strathmann, 2002). Regardless, the effects of offspring size on the onset of metamorphic competence and the onset of indiscriminate settlement behaviour is likely to result in large and small offspring having very different dispersal profiles.…”

Earliest ciliary swimming effects vertical transport of planktonic embryos in turbulence and shear flow

“…However, early embryos are likely to be dispersed away from the immediate vicinity of adult spawning grounds by the time they become motile (on the order of 20h after fertilization for temperate echinoderms) (e.g. Staver and Strathmann, 2002), so differences in species' depth distributions may be more relevant to the question of adaptive differences in swimming performance. Strongylocentrotus purpuratus and D. excentricus do occupy quite different habitat types as adults, but both species are common at shallow depths (<30m).…”

“…Embryos of many different broadcast spawners develop rapidly to swimming and have a passively maintained upward orientation (Staver and Strathmann, 2002) that could enable migration away from the benthos. Ciliated early embryos are generally quite small (<0.3mm diameter) and are weak swimmers, capable of maximum upward speeds in the range of 1.5-6.0ϫ10 ; Table1).…”