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

Abstract

Theory predicts that the maintenance of haplodiplontic life cycles requires ecological differences between the haploid gametophytes and diploid sporophytes, yet evidence of such differences remain scarce. The haplodiplontic red seaweed Gracilaria vermiculophylla has invaded the temperate estuaries of the Northern Hemisphere, where it commonly modifies detrital and trophic pathways. In native populations, abundant hard substratum enables spore settlement, and gametophyte:tetrasporophyte ratios are ~40:60. In contrast, many non-native populations persist in soft-sediment habitats without abundant hard substratum, and can be 90%-100% tetrasporophytic. To test for ecologically relevant phenotypic differences, we measured thallus morphology, protein content, organic content, "debranching resistance" (i.e., tensile force required to remove a branch from its main axis node), and material properties between male gametophytes, female gametophytes, and tetrasporophytes from a single, nonnative site in Charleston Harbor, South Carolina, USA in 2015 and 2016. Thallus length and surface area to volume ratio differed between years, but were not significantly different between ploidies. Tetrasporophytes had lower protein content than gametophytes, suggesting the latter may be more attractive to consumers. More force was required to pull a branch from the main axis of tetrasporophytes relative to gametophytes. A difference in debranching resistance may help to maintain tetrasporophyte thallus durability relative to gametophytes, providing a potential advantage in free-floating populations. These data may shed light on the invasion ecology of an important ecosystem engineer, and may advance our understanding of life cycle evolution and the maintenance of life cycle diversity.

Using RAD‐seq to develop sex‐linked markers in a haplodiplontic alga

“…Red algal female gametophytes invest a substantial amount of energy in nurturing developing zygotes and carpospores in the carposporophyte (Searles 1980), which may explain these results (see also Lees et al. 2018). Thus, ecophysiological studies based on reproductive material, often by necessity, may obscure differences among life cycle stages in response to different biotic or abiotic factors.…”

“…The four female thalli were sampled in 2016 (see Lees et al. 2018). (b) Example gel with positive and negative controls and four thalli from 2015 that were identified as vegetative (FJS_63, FJS_84, FJS_87) and one as a tetrasporophyte (FJS_91).…”

Predicting benthic macroalgal abundance in shallow coastal lagoons from geomorphology and hydrologic flow patterns

“…In this study, we focus on predicting macroalgae on intertidal flats in shallow coastal lagoons. To recruit and develop into the adult life cycle stage, all macroalgae require hard substrate, which is limited in soft‐sediment coastal lagoons (Thomsen and McGlathery 2005; Krueger‐Hadfield et al 2016; Lees et al 2018). Macroalgae can be found fixed by a holdfast to hard substrate when it is available in soft‐sediments (Krueger‐Hadfield et al 2016); such as on oyster reefs and shell fragments (Thomsen et al 2006).…”

Incorporating Ploidy Diversity into Ecological and Community Genetics

“…For example, Lees et al. () found Agarophyton vermiculophyllum tetrasporophytes had lower protein content and stronger thalli, perhaps leading to diploid dominance in free‐floating, non‐native populations (Krueger‐Hadfield et al. ).…”