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We conducted a population genetic analysis of the stalked kelp,Pterygophora californica, in the Santa Barbara Channel, California,USA. The results were compared with previous work on the genetic differentiation of giant kelp,Macrocystis pyrifera,in the same region. These two sympatric kelps not only share many life history and dispersal characteristics but also differ in that dislodgedP. californicadoes not produce floating rafts with buoyant fertile sporophytes, commonly observed forM. pyrifera. We used a comparative population genetic approach with these two species to test the hypothesis that the ability to produce floating rafts increases the genetic connectivity among kelp patches in the Santa Barbara Channel. We quantified the association of habitat continuity and oceanographic distance with the genetic differentiation observed in stalked kelp, like previously conducted for giant kelp. We compared both overall (across all patches) and pairwise (between patches) genetic differentiation. We found that oceanographic transit time, habitat continuity, and geographic distance were all associated with genetic connectivity inP. californica, supporting similar previous findings forM. pyrifera. Controlling for differences in heterozygosity between kelp species using Jost'sDEST, we showed that global differentiation and pairwise differentiation were similar among patches between the two kelp species, indicating that they have similar dispersal capabilities despite their differences in rafting ability. These results suggest that rafting sporophytes do not play a significant role in effective dispersal ofM. pyriferaat ecologically relevant spatial and temporal scales.
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Individual and population‐level variation in susceptibility to temperature in early life history stages of giant kelp
Abstract Because foundation species create structure in a community, understanding their ecological and evolutionary responses to global change is critical for predicting the ecological and economic management of species and communities that rely on them. Giant kelp (Macrocystis pyrifera) is a globally distributed foundation species with seasonal fluctuations in abundance in response to local nutrient levels, storm intensity, and ocean temperatures. Here we examine genetic variation in individual and population‐level responses of early life history stages (zoospore settlement, survival, and gametogenesis) to increased temperatures to determine the potential for natural selection on temperature‐tolerant individuals that would allow adaptation to a changing climate. We collected fertileM. pyriferasporophyll blades from three sites along the California coast (Los Angeles, Santa Barbara, Monterey Bay) and induced zoospore release in the lab. Spores settled on microscope slides at three treatment temperatures (16, 20, and 22°C), matured for 21 days, and were imaged weekly to determine settlement, survival, and maturation success. On average, individuals from all sites showed lower rates of settlement and maturation in response to increasing temperature. However, the magnitude of the responses to temperature varied among populations. Survival tended to increase with temperature in Los Angeles and Santa Barbara populations but decreased with increasing temperature for the Monterey Bay population. We observed little genetic variation in temperature responses among individuals within sites, suggesting little scope for evolution within populations to increase the resilience ofM. pyriferapopulations to warming ocean temperatures and predicted declines in kelp abundance. Yet sufficient dispersal among populations could allow for adaptation of early life history traits among populations via evolutionary rescue of declining populations.
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- Award ID(s):
- 1754449
- PAR ID:
- 10442148
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Marine Ecology
- Volume:
- 44
- Issue:
- 6
- ISSN:
- 0173-9565
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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