Closer to the rear edge: ecology and genetic diversity down the core‐edge gradient of a marine macroalga

Abstract

Abstract. A fundamental goal in ecology is to understand distribution and abundance of species.Peripheral populations inhabiting the trailing-edge of a species' distribution may carry considerable ecological and evolutionary value yet being most threatened under predicted climate change scenarios. However, the nature of species distributional limits and the ecological and genetic implications of living at low latitude rear edges remain unclear. The assumption that population abundance declines towards range edges, where environmental selective pressure increases, is the basis of a wide range of ecological and evolutionary predictions. Empirical data have provided contrasting evidence about the consequences of living at low latitude distributional limits, raising concerns regarding their generality and highlighting the need for combined multidisciplinary tests. Here, we provide a long-term, comprehensive evaluation of latitudinal patterns in genetic diversity, demographic, morphological and life history traits in the marine macroalga Fucus guiryi.The center to edge transition was mirrored by increasing water and air temperature gradients, with sea surface temperature of coldest months being the most relevant influence on F. guiryi traits. Overall, we identified a strong correlation between ecological data, collected over one year at bimonthly intervals, and distance to the range center. We found decreasing population and individual size towards distributional margins. Similarly, reproductive capacity, threshold size for reproduction, density of reproductive population and recruitment rates showed a core to edge reduction. Temporal variability of individual reproductive effort and recruitment rates did not conform to the general pattern. In contrast, population genetic data did not show a core-edge gradient, as gene diversity and allelic richness were not significantly lower at edge populations, contradicting predictions of higher drift and bottlenecks for smaller edge populations.The contrasting support provided by genetic and ecological data highlights the need to combine multiple and cross-disciplinary evidence for a comprehensive understanding of ecological and evolutionary mechanisms linked to species ranges.

Phenotypic plasticity at the edge: Contrasting population‐level responses at the overlap of the leading and rear edges of the geographical distribution of two Scurria limpets

“…zebrina , was significantly different from populations inside the range of either species. In agreement with theoretical expectations the plastic, between‐site, phenotypic responses for the species at the leading edge of its range were gradient‐like or did not show significant differences, while the response of rear edge populations was site‐specific (Lourenco et al., ; Nicastro et al., ; Zardi et al., ). Together with the heterogeneous and extreme physical and chemical conditions, we documented in the intertidal and coastal zone around PLV (i.e.…”

Taking the heat: distinct vulnerability to thermal stress of central and threatened peripheral lineages of a marine macroalga

“…The Atlantic Iberian coastline is characterized by a strong north‐to‐south gradient of increasing water and air temperature, which is persistent throughout the whole year (Lima & Wethey, ; Zardi et al ., ). Notably, over the last three decades, coastal water temperatures have increased significantly along the entire coastline, averaging 0.20 °C/decade (Nicastro et al ., ).…”

“…Cabral et al ., ). Additionally, intertidal sites inhabited by F. vesiculosus within Portuguese estuaries are largely marine dominated (Zardi et al ., ). In general, they are characterized by smaller amplitude thermal fluctuations compared to the open coast.…”

Explaining Ocean Warming: Causes, scale, effects and consequences

“…Fucoid abundance is largely determined by the success rate of propagules "escaping" from grazers such as limpets, which is more likely among dense cover of Semibalanus balanoides barnacles as they restrict gastropod movement and provide refuges for juvenile plants (Hawkins, 1981;Hartnoll and Hawkins, 1985;Johnson et al, 1997Johnson et al, , 1998aBurrows and Hawkins, 1998). Fucoid canopy cover is predicted to decline in response to climate change (Box 3.7.4 Figure 2) due to a combination of greater physiological stress (Pearson et al, 2009;Martínez et al, 2012;Ferreira et al, 2014;Zardi et al, 2015) and increased grazing pressure (Jenkins et al, 2001Ferreira et al, 2015). At mid-latitudes in particular, escape rates are predicted to decline due to a combination of reduced recruitment in drier summers (Ferreira et al, 2015), greater grazing pressure as southern species of limpets and trochids increase in abundance and ranges extend further north (Southward et al, 1995;Mieszkowska et al, 2006), and reduced barnacle density as populations of Semibalanus balanoides are replaced by slowergrowing Chthamalus species Poloczanska et al, 2008).…”