Reproductive and electrophoretic evidence for genetic maintenance of dimorphism in the ascidian<i>Pyura stolonifera</i>near Melbourne, Australia

Dalby, J. E.

doi:10.1080/00785236.1997.10428673

Cited by 15 publications

(18 citation statements)

References 56 publications

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“…In colonial ascidians, important intraspecific differences in life-history parameters (genetically determined) have been described for Botryllus schlosseri (Grosberg 1988, Yund et al 1997, while in other instances divergence in biological parameters support the existence of cryptic speciation (Degnan & Levin 1995, Dalby 1997a, De Caralt et al 2002. In our case, the 2 morphotypes studied featured significant differences in biological traits.…”

Section: Discussionmentioning

confidence: 60%

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Life cycles and growth rates of two morphotypes of Cystodytes (Ascidiacea) in the western Mediterranean

López‐Legentil¹,

Ruchty²,

Domenech³

et al. 2005

Mar. Ecol. Prog. Ser.

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The reproductive cycles, growth and survival of the 2 most abundant color morphs (blue and purple) of the colonial ascidian Cystodytes occurring in the western Mediterranean were studied over a period of 20 mo. Previous reports have assigned the 2 morphotypes to the nominal species C. dellechiajei. A seasonal pattern emerged, in which larval release occurred in late spring and summer, followed by a period of active growth. Significant differences between morphotypes were also detected: the cycles of both reproduction and growth rates of the purple morph lagged 1 to 2 mo behind those of the blue morph. Within morphotypes, the time course of reproductive activity and growth rates also displayed a temporal lag that suggests partitioning of resources to either reproduction or growth. In particular, the growth rates of the 2 morphotypes peaked when reproductive activity was at its lowest. There were no significant differences in mortality between these forms, and in both cases a significant negative correlation was found between mortality and size. In the blue morph, maximal growth rate was negatively correlated with size, whilst no significant relationship between growth rate and size was detected in the purple morph. There were no significant differences in growth between colonies of the purple morph that were in contact with the toxic sponge Crambe crambe and those that were not. The differences found in the reproductive cycles of these 2 morphotypes match previously reported genetic and chemical divergences.

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Section: Discussionmentioning

confidence: 60%

“…In some cases, color varieties have been shown to correspond to different species (Dalby 1997a,b, Tarjuelo et al 2004), but not in others (Sabbadin 1982). The overwhelming message from molecular studies is that sibling and cryptic speciation phenomena are much more abundant in marine species than previously thought (Knowlton 2000).…”

Section: Discussionmentioning

confidence: 95%

Life cycles and growth rates of two morphotypes of Cystodytes (Ascidiacea) in the western Mediterranean

López‐Legentil¹,

Ruchty²,

Domenech³

et al. 2005

Mar. Ecol. Prog. Ser.

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“…In such cases, only molecular tools can reliably identify and uncover a cryptic introduction. Not surprisingly, instances of cryptic introduction and speciation have been shown whenever ascidian species with variable morphology and wide distribution ranges have been studied with molecular markers (Aron & Solé‐Cava 1991; Dalby 1997; Tarjuelo et al . 2001, 2004; Castilla et al .…”

Section: Introductionmentioning

confidence: 99%

Genetic structure of the star sea squirt, Botryllus schlosseri, introduced in southern European harbours

2006

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The introduction of new genetic variants or species is often caused by maritime transport between harbours. Botryllus schlosseri is a cosmopolitan ascidian species that is found in both harbours and open shore habitats. In order to determine the influence of ship traffic on the genetic structure and phylogeography of B. schlosseri in southern Europe, we analyzed the variability of a fragment of the mitochondrial gene cytochrome c oxidase subunit I (COI). We sampled seven Atlanto-Mediterranean harbour populations and three open-shore populations. In addition, we sequenced some colonies from the US-Atlantic coast and from other Mediterranean localities to perform phylogenetic analyses. Although the number of polymorphic sites recorded (25.8%) was within the range observed in other population studies based on ascidian COI sequences, the haplotypic diversity (16 haplotypes out of 181 sequences) was much lower. Moreover, a lack of intermediate haplotypes was observed. This pattern of high nucleotide diversity and low haplotype diversity was consistent with introduction events of a few divergent haplotypes. We found a strong genetic structure in the study populations. Gene flow was only appreciable between some harbour populations. Harbour- and open-shore populations were well differentiated, although there was no evidence for isolation by distance. A nested clade analysis pointed to long-distance colonization, possibly coupled with subsequent fragmentation, as the underlying process. Our results suggest that B. schlosseri entered the study area via harbour-hopping, possibly through recurrent introduction events. The haplotypes from North America and most of the European ones were grouped in the same phylogenetic clade. This suggests occasional gene flow between both continents, probably through ship transport.

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“…Genetic studies of species boundaries in ascidians are similarly limited, with only a few genera emerging from bibliographic searches: Botryllus (Aron & Solé-Cava, 1991), Pyura (Dalby, 1997) and Herdmania (Degnan & Lavin, 1995). In each of these cases, the species could be readily distinguished by color or other features, and genetic differences were substantial.…”

Section: Other Marine Invertebratesmentioning

confidence: 99%

Molecular genetic analyses of species boundaries in the sea

2000

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The tools of molecular genetics have enormous potential for clarifying the nature and age of species boundaries in marine organisms. Below I summarize the genetic implications of various species concepts, and review the results of recent molecular genetic analyses of species boundaries in marine microbes, plants, invertebrates and vertebrates. Excessive lumping, rather than excessive splitting, characterizes the current systematic situation in many groups. Morphologically similar species are often quite distinct genetically, suggesting that conservative systematic traditions or morphological stasis may be involved. Some reproductively isolated taxa exhibit only small levels of genetic differentiation, however. In these cases, large population sizes, slow rates of molecular evolution, and relatively recent origins may contribute to the difficulty in finding fixed genetic markers associated with barriers to gene exchange. The extent to which hybridization blurs species boundaries of marine organisms remains a subject of real disagreement in some groups (e.g. corals). The ages of recently diverged species are largely unknown; many appear to be older than 3 million years, but snails and fishes provide several examples of more recent divergences. Increasingly sophisticated genetic analyses make it easier to distinguish allopatric taxa, but criteria for recognition at the species level are highly inconsistent across studies. Future molecular genetic analyses should help to resolve many of these issues, particularly if coupled with other biological and paleontological approaches.

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Reproductive and electrophoretic evidence for genetic maintenance of dimorphism in the ascidianPyura stoloniferanear Melbourne, Australia

Cited by 15 publications

References 56 publications

Life cycles and growth rates of two morphotypes of Cystodytes (Ascidiacea) in the western Mediterranean

Life cycles and growth rates of two morphotypes of Cystodytes (Ascidiacea) in the western Mediterranean

Genetic structure of the star sea squirt, Botryllus schlosseri, introduced in southern European harbours

Molecular genetic analyses of species boundaries in the sea

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