Biology subjects

Oetterer, A.

Publications and source records attributed to Oetterer, A..

2 recordsLinked to original sources

bioRxiv2025

A CLONAL LEGACY? REPRODUCTIVE MODE VARIATION IN HARD AND SOFT BOTTOM GRACILARIA VERMICULOPHYLLA POPULATIONS

The red macroalga Gracilaria vermiculophylla invasion provides an opportunity to investigate the evolution of biphasic life cycles and of reproductive modes by understanding how they structure and contribute colonizing new environments in natural conditions. In hard bottom habitats, we find gametophytes and tetrasporophytes fixed by holdfasts to hard substrates, whereas in soft bottom habitats, we find free-living tetrasporophytes either drifting or anchored by tube-building polychaetes. We collected thalli from hard and soft bottom habitats along the Eastern Shore of Virginia and Maryland to investigate the role of substrate on life cycle and reproductive mode dynamics. We determined the phase and sex using observable reproductive structures and a sex-linked PCR assay, followed by genotyping all thalli using nine microsatellite loci. Sexual reproduction prevailed in hard bottom sites, whereas clonal (asexual) reproduction dominated soft bottom sites and was accompanied by tetrasporophytic dominance. There was site-specific variation in selfing and clonal rates that are supported by observations of physiological stress and local extirpation, such as at Ape Hole Creek and Fowling Point, respectively. We found evidence of isolation by distance and the structuring of genetic diversity by habitat type, then site, and finally by year. While broad patterns have been described across the extant range, we clarify population genetic patterns in hard versus soft bottom habitats that are not confounded by the invasion history comparing native and non-native thalli. These results have implications for the on-going spread of this alga and contribute to our understanding of the population genetics of partially clonal taxa.

evolutionary biology↗

bioRxiv2025

THE HARD AND SOFT OF IT: THE ROLE OF SUBSTRATE IN PATTERNS OF PHASE DOMINANCE AND PHENOLOGY IN GRACILARIA VERMICULOPHYLLA

Despite the importance of the seasonal timing of life cycle events for understanding population dynamics, we lack information on the phenology of most macroalgal species. The red macroalga Gracilaria vermiculophylla is now common in both hard and soft bottom habitats following its invasion throughout the Northern Hemisphere. In sites with sufficient hard substratum, thalli are fixed by holdfasts to hard substrate. By contrast, in sites with soft substratum, thalli are free-living and either drift free-floating or anchored by the tube building polychaete Diopatra cuprea. The difference in substrate type has profound implications on the evolutionary ecology of G. vermiculophylla populations whereby the life cycle is disrupted in soft bottom habitats leading to tetrasporophytic dominance. To investigate these patterns across seasons, we determined the reproductive state via microscopy and phase via a sex-linked PCR assay for >4,800 thalli over the course of three years at hard and soft bottom sites with fixed and free-living G. vermiculophylla thalli, respectively, along the Eastern Shore of Virginia and Maryland. At hard bottom sites, most thalli were reproductive in the summer and sites were composed of gametophytes and tetrasporophytes, though there was a tetrasporophytic bias. By contrast, soft bottom sites were overwhelming tetrasporophyte dominated and fewer thalli were reproductive at any point in the year. Moreover, each soft bottom site displayed different patterns in the proportion of reproductive thalli, with G. vermiculophylla abundance fluctuating through time. Phenology surveys critical for understanding the spread of introduced macroalgae, including the on-going spread of G. vermiculophylla.

evolutionary biology↗