Invasion of novel habitats uncouples haplo‐diplontic life cycles

Abstract

Baker's Law predicts uniparental reproduction will facilitate colonization success in novel habitats. While evidence supports this prediction among colonizing plants and animals, few studies have investigated shifts in reproductive mode in haplo-diplontic species in which both prolonged haploid and diploid stages separate meiosis and fertilization in time and space. Due to this separation, asexual reproduction can yield the dominance of one of the ploidy stages in colonizing populations. We tested for shifts in ploidy and reproductive mode across native and introduced populations of the red seaweed Gracilaria vermiculophylla. Native populations in the northwest Pacific Ocean were nearly always attached by holdfasts to hard substrata and, as is characteristic of the genus, haploid-diploid ratios were slightly diploid-biased. In contrast, along North American and European coastlines, introduced populations nearly always floated atop soft-sediment mudflats and were overwhelmingly dominated by diploid thalli without holdfasts. Introduced populations exhibited population genetic signals consistent with extensive vegetative fragmentation, while native populations did not. Thus, the ecological shift from attached to unattached thalli, ostensibly necessitated by the invasion of soft-sediment habitats, correlated with shifts from sexual to asexual reproduction and slight to strong diploid bias. We extend Baker's Law by predicting other colonizing haplo-diplontic species will show similar increases in asexuality that correlate with the dominance of one ploidy stage. Labile mating systems likely facilitate colonization success and subsequent range expansion, but for haplo-diplontic species, the long-term eco-evolutionary impacts will depend on which ploidy stage is lost and the degree to which asexual reproduction is canalized.

Population genomics of the introduced and cultivated Pacific kelp Undaria pinnatifida: Marinas—not farms—drive regional connectivity and establishment in natural rocky reefs

“…Other marine species have shown differences amongst populations inhabiting different habitat types. For example, differences were found between natural reefs and hatcheries in the Manila clam Ruditapes philippinarum (Xing, Gao, & Li, 2014), between enclosed and open marinas in the invasive tunicate Styela clava (Dupont, Viard, Dowell, Wood, & Bishop, 2009), or between fixed and free‐floating populations of the invasive red seaweed Gracilaria vermiculophylla (Krueger‐Hadfield et al., 2016). Here, farmed populations were highly distinct from the other types of populations because, for a given sampling year, they displayed the lowest genetic diversity, and showed no inbreeding signal (negative F IS , Figure 2a).…”

“…This kelp displays a haploid–diploid life cycle, consisting of a large diploid sporophyte phase alternating with a microscopic haploid gametophyte phase. Conversely to other invasive seaweeds with a similar life cycle (e.g., Gracillaria vermiculophylla ; Krueger‐Hadfield et al., 2016), there is no evidence of vegetative reproduction in introduced populations of U. pinnatifida but it is a self‐compatible sexually reproducing species, a trait that may facilitate colonization of new habitats (Pannell et al., 2015). In addition, it displays high fecundity and a short generation time (e.g., two generations per year in Brittany [north western France], Castric‐Fey, Beaupoil, Bouchain, Pradier, & L'Hardy‐Halos, 1999).…”

Mitochondrial diversity inGonionemus(Trachylina:Hydrozoa) and its implications for understanding the origins of clinging jellyfish in the Northwest Atlantic Ocean

“…Similarly, it is possible that contemporary NWA populations may be experiencing rapid adaptive evolution. However, detection of adaptation can be obscured by phenotypic plasticity (Tepolt, 2015; Krueger-Hadfield et al, 2016). Thus, future studies that use nuclear markers capable of finer-scale resolution and detection of hybridization, coupled with phenotypic characterization in Pacific and NWA regions, are necessary to assess both the lineage admixture and adaptive evolution hypotheses in Gonionemus .…”

“…Accordingly, many species are considered cryptogenic and cannot be classified as introduced or native with confidence (Carlton, 1996). In some instances, organisms may exhibit different phenotypes in their introduced range than in their native range (Miglietta & Lessios, 2009; Krueger-Hadfield et al, 2016), making morphology-based identifications difficult. Molecular approaches can be very useful in identifying non-native taxa (Geller, Darling & Carlton, 2010), but results are also not always clear-cut.…”

Nonnative Gracilaria vermiculophylla tetrasporophytes are more difficult to debranch and are less nutritious than gametophytes

“…, Krueger‐Hadfield et al. ), making them good candidates for testing the role of ecological differentiation in maintaining haplodiplontic life cycles. Typically, meiosis occurs within the tetrasporangia on the tetrasporophyte, producing haploid tetraspores.…”