Temperature Effects on Gametophyte Life-History Traits and Geographic Distribution of Two Cryptic Kelp Species

Abstract

A major determinant of the geographic distribution of a species is expected to be its physiological response to changing abiotic variables over its range. The range of a species often corresponds to the geographic extent of temperature regimes the organism can physiologically tolerate. Many species have very distinct life history stages that may exhibit different responses to environmental factors. In this study we emphasized the critical role of the haploid microscopic stage (gametophyte) of the life cycle to explain the difference of edge distribution of two related kelp species. Lessonia nigrescens was recently identified as two cryptic species occurring in parapatry along the Chilean coast: one located north and the other south of a biogeographic boundary at latitude 29–30°S. Six life history traits from microscopic stages were identified and estimated under five treatments of temperature in eight locations distributed along the Chilean coast in order to (1) estimate the role of temperature in the present distribution of the two cryptic L. nigrescens species, (2) compare marginal populations to central populations of the two cryptic species. In addition, we created a periodic matrix model to estimate the population growth rate (λ) at the five temperature treatments. Differential tolerance to temperature was demonstrated between the two species, with the gametophytes of the Northern species being more tolerant to higher temperatures than gametophytes from the south. Second, the two species exhibited different life history strategies with a shorter haploid phase in the Northern species contrasted with considerable vegetative growth in the Southern species haploid stage. These results provide strong ecological evidence for the differentiation process of the two cryptic species and show local adaptation of the life cycle at the range limits of the distribution. Ecological and evolutionary implications of these findings are discussed.

Species are hypotheses: avoid connectivity assessments based on pillars of sand

“…Ecological differentiation between the two cryptic species was investigated, using different approaches (e.g. controlled response to different thermal and desiccation stresses in the laboratory, Oppliger et al 2012;L opez-Cristoffanini et al 2013). Both microscopic (haploid) and macroscopic (diploid) phases of the kelp life cycle were studied.…”

The importance of phenotypic plasticity and local adaptation in driving intraspecific variability in thermal niches of marine macrophytes

“…Consequently, our dataset did not include in situ field observations of differential performance, morphology, phenology or other life history traits (Araújo et al 2011, Andrews et al 2014. We also omit studies dealing with two cryptic species (Oppliger et al 2012) or those that were confounded by other covarying environmental gradients. Therefore, studies from the Baltic Sea (Tatarenkov et al 2005, Lago-Lestón et al 2010 were not included due to the confounding salinity gradient that can invoke other distinct physiological ecotypes (Karsten 2012).…”

Management and conservation of the kelp speciesLaminaria digitata: using genetic tools to explore the potential exporting role of the MPA “Parc naturel marin d’Iroise”

“…Finally, evidence indicates that southern Brittany populations of L. digitata show high interannual variability regarding population size: (i) theoretically, marginal populations are often small and subject to bottlenecks (Eckert et al 2008); (ii) southern distribution of L. digitata might be constrained by overheating of North Atlantic waters (Arzel 1998); and (iii) field surveys carried out by the authors during the last decade also point to fluctuations in their demographic structure (unpublished data). However, it is important to remind that, while L. digitata displays a life-history alternating between two independent generations (a macroscopic diploid sporophyte and a microscopic haploid gametophyte), demographic data often focus on the macroscopic forms (but see Oppliger et al 2012). Thus, populations might persist and self-sustain even when sporophytes have completely disappeared.…”