Evolutionary Transitions in Mode of Development

Abstract

In the large body of literature on ecological and evolutionary mechanisms underlying transitions between planktotrophy and lecithotrophy, the focus has typically covered long evolutionary timescales; that is, evolution of complex larval traits is generally discussed in the context of phylogenetic patterns detectable at the level of families, classes, or phyla. An analytical approach incorporating comparative phylogenetics is increasingly used to address these long-view questions. Here, we discuss what has been learned from taking a comparative phylogenetic approach and the limitations of this approach. We propose that approaches based on a closer view—that is, analyses that focus on genetic, morphological, and functional variation among individuals, populations, or closely related congeners—have greater potential to answer questions about mechanisms underlying the loss and regain of major complex characters such as feeding larvae.

Ancestral form and function of larval feeding structures are retained during the development of non-planktotrophic gastropods

“…As currently understood, the predominant direction of evolutionary change in MOD is from species with planktotrophic larvae to those with direct development; and it is thought to be uncommon or virtually impossible for planktotrophic larvae to evolve from species with direct development without being obviously distinct from the ancestral planktotrophic form (Strathmann 1978a, b). There are two main lines of evidence that support this idea: (1) The complex structures used for larval feeding and swimming are generally lost, reduced or modified in species with direct development, and (2) phylogenetic reconstructions of changes in MOD tend to suggest that the presence of a pelagic larva is ancestral, and that direct development evolves repeatedly towards the tips of the trees (Krug et al 2015;Collin and Moran 2018). This provides evidence for multiple origins of direct development in each group (e.g., Duda and Palumbi 1999;Hart and Podolsky 2005;Byrne 2006;Krug et al 2015;but see Jeffery et al 2003).…”

“…It is common for embryos of gastropod species lacking pelagic larvae and some lecithotrophic (i.e., nonfeeding) annelid larvae to retain larval features such as the velum (in gastropods) and the opposed band ciliary mechanism used for feeding and swimming (Fioroni 1967;Moran 1999;Pernet 2003; Hofstee and Pernet 2011; Pernet 2020). In addition, the high proportion of species with non-planktotrophic development makes phylogenetic reconstructions of the direction of evolutionary transitions in development uncertain (Collin 2004;Collin and Moran 2018) and highly dependent on the assumptions about the transition probabilities and outgroup coding (Rouse 2000a,b;Collin 2004;Li and Foighil 2015). The interpretation of these comparative patterns is further complicated by the possibility of differential speciation and extinction of species with different modes of development (Krug et al 2015).…”

“…Mode of development (MOD) in marine invertebrates is one such key feature thought to influence both the rate and direction of evolution (Krug et al 2015;Collin and Moran 2018).…”

Early development in Kelletia kelletii (Forbes, 1850) (Gastropoda: Buccinidae), an Eastern Pacific gastropod with planktonic larvae

“…A los 20 d, o cerca de los 20 d, las velígeras en etapa tardía eran velígeras nadadoras descapsuladas que (Duclos, 1832) (Romero et al 2004) and Amphissa versicolor Dall, 1871 (Page and Parries 2000). Dense taxon sampling is necessary within the Buccinidae, and other gastropod groups, for phylogenetic analyses that can elucidate the evolution and distribution of larval developmental mode (Collin and Moran 2018). Of course, such studies are only as good as the larval data examined with the phylogeny.…”

“…With few exceptions, documentation of larval development, and particularly larval morphology, in buccinid gastropods is lacking, especially for taxa with planktonic larvae. Accounts of detailed larval characteristics across this diverse family could inform studies of larval development, larval ecology, and developmental evolution (Collin and Moran 2018). Thus, this study is intended to complement the work that has documented much of early ontogeny in K. kelletii Herrlinger 1981).…”