Extant or extinct tipping points - climate changes drive genetic diversity and dynamics of range edge populations as evolutionary hotspots

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Publications

Interactions of daylength, temperature and nutrients affect thresholds for life stage transitions in the kelp Laminaria digitata (Phaeophyceae)

Publication . Martins, Neusa; Tanttu, Heidi; Pearson, Gareth; Serrao, Ester A.; Bartsch, Inka

Kelp beds worldwide are under pressure from ongoing climate and environmental change. Along European coastlines increases in seawater temperature and changes in nutrient conditions occur where upwelling events are disrupted and also along eutrophicated coasts. In addition, seaweed responses to change may interact with seasonal daylength cycles. We performed a factorial experiment to examine the combined effects of seawater temperatures, nutrient regimes and photoperiod (long and short days) in order to better understand how latitudinal or seasonal differences in daylengths affect the sensitivity of transient microscopic kelp stages of Laminaria digitata from the North Sea to warming and eutrophication. While the optimal temperature range for vegetative gametophyte growth was 10 degrees C-18 degrees C under long summer photoperiod conditions, gametogenesis was induced at lower temperatures between 5 degrees C and 15 degrees C, with maximum sporophyte development under long photoperiods and enriched nutrient regimes, which represent local late spring conditions. Although gametogenesis was fastest at 10 degrees C-15 degrees C, sporophyte recruitment was highest at 5 degrees C. As these particular early life cycle processes in L. digitata have different temperature optima, this may drive the seasonal cycle of recruitment in the field. Increasing summer temperatures due to global warming will increase gametophyte size due to enhanced vegetative growth and inhibition of gametogenesis. This will probably lead to delayed but enhanced recruitment of new sporophytes under cooler autumn to spring conditions over a wide geographical scale, preventing the formation of juvenile sporophytes under stressful summer conditions and possibly changing annual recruitment patterns.

2017-04Journal article

Open Access

Major shifts at the range edge of marine forests: the combined effects of climate changes and limited dispersal

Publication . Assis, J.; Berecibar, E.; Claro, B.; Alberto, F.; Reed, D.; Raimondi, P.; A, Serrão

Global climate change is likely to constrain low latitude range edges across many taxa and habitats. Such is the case for NE Atlantic marine macroalgal forests, important ecosystems whose main structuring species is the annual kelp Saccorhiza polyschides. We coupled ecological niche modelling with simulations of potential dispersal and delayed development stages to infer the major forces shaping range edges and to predict their dynamics. Models indicated that the southern limit is set by high winter temperatures above the physiological tolerance of overwintering microscopic stages and reduced upwelling during recruitment. The best range predictions were achieved assuming low spatial dispersal (5 km) and delayed stages up to two years (temporal dispersal). Reconstructing distributions through time indicated losses of similar to 30% from 1986 to 2014, restricting S. polyschides to upwelling regions at the southern edge. Future predictions further restrict populations to a unique refugium in northwestern Iberia. Losses were dependent on the emissions scenario, with the most drastic one shifting similar to 38% of the current distribution by 2100. Such distributional changes might not be rescued by dispersal in space or time (as shown for the recent past) and are expected to drive major biodiversity loss and changes in ecosystem functioning.

2017-03Journal article

Open Access

Host and Environmental Specificity in Bacterial Communities Associated to Two Highly Invasive Marine Species (Genus Asparagopsis)

Publication . Aires, Tânia; Serrão, Ester; Engelen, Aschwin H.

As habitats change due to global and local pressures, population resilience, and adaptive processes depend not only on their gene pools but also on their associated bacteria communities. The hologenome can play a determinant role in adaptive evolution of higher organisms that rely on their bacterial associates for vital processes. In this study, we focus on the associated bacteria of the two most invasive seaweeds in southwest Iberia (coastal mainland) and nearby offshore Atlantic islands, Asparagopsis taxiformis and Asparagopsis armata. Bacterial communities were characterized using 16S rRNA barcoding through 454 next generation sequencing and exploratory shotgun metagenomics to provide functional insights and a backbone for future functional studies. The bacterial community composition was clearly different between the two species A. taxiformis and A. armata and between continental and island habitats. The latter was mainly due to higher abundances of Acidimicrobiales, Sphingomonadales, Xanthomonadales, Myxococcales, and Alteromonadales on the continent. Metabolic assignments for these groups contained a higher number of reads in functions related to oxidative stress and resistance to toxic compounds, more precisely heavy metals. These results are in agreement with their usual association with hydrocarbon degradation and heavy-metals detoxification. In contrast, A. taxiformis from islands contained more bacteria related to oligotrophic environments which might putatively play a role in mineralization of dissolved organic matter. The higher number of functional assignments found in the metagenomes of A. taxiformis collected from Cape Verde Islands suggest a higher contribution of bacteria to compensate nutrient limitation in oligotrophic environments. Our results show that Asparagopsis-associated bacterial communities have host-specificity and are modulated by environmental conditions. Whether this environmental effect reflects the host's selective requirements or the locally available bacteria remains to be addressed. However, the known functional capacities of these bacterial communities indicate their potential for eco-physiological functions that could be valuable for the host fitness.

2016-04Journal article

Open Access

Role of spawning synchrony on hybridization barriers in sympatric intertidal fucoid algae - when and why

Publication . Monteiro, Carla Alexandra da Silva; Pearson, Gareth; Serrão, Ester; Valero, Myriam

In sympatric assemblages of congeners with incomplete reproductive barriers, the synchrony within species and asynchrony between species may be under strong selection, reinforcing prezygotic reproductive isolation and reducing hybridization. Interspecific asynchrony and gametic incompatibility are considered the two most important prezygotic mechanisms reinforcing assortative mating and acting against hybridization. However, divergence of reproductive strategies in closely related species might also contribute to reproductive isolation. The main goal of this thesis was to investigate hypotheses concerning the mechanisms that act against hybridization in sympatric species with external fertilization, including the asynchrony of gamete release, mating system variations and gametic incompatibility. As a model we used sympatric Fucus species with different reproductive modes, hermaphroditic (selfing) and dioecious (obligate outcrossing). The results show a clear relationship between patterns of gamete release and tidal/circadian cycles that contributes to interspecific variation in spawning time between hermaphroditic and dioecious species. The data support the hypothesis that asynchronous egg release acts as a prezygotic barrier to hybridization between hermaphroditic and dioecious species, and therefore, that mating system variation between congeners plays important role against hybridization. We also provide evidence that gametic incompatibility is an incomplete prezygotic barrier between Fucus species. Results show the potential of interspecific fertilization, and the potential growth and survival of hybrids relative to the parental lineage.

2016-07-07Doctoral thesis

Open Access

Future climate change is predicted to shift long-term persistence zones in the cold-temperate kelp Laminaria hyperborea

Publication . Assis, J.; Lucas, Ana Vaz; Bárbara, Ignacio; Serrão, Ester

Global climate change is shifting species distributions worldwide. At rear edges (warmer, low latitude range margins), the consequences of small variations in environmental conditions can be magnified, producing large negative effects on species ranges. A major outcome of shifts in distributions that only recently received attention is the potential to reduce the levels of intra-specific diversity and consequently the global evolutionary and adaptive capacity of species to face novel disturbances. This is particularly important for low dispersal marine species, such as kelps, that generally retain high and unique genetic diversity at rear ranges resulting from long-term persistence, while ranges shifts during climatic glacial/interglacial cycles. Using ecological niche modelling, we (1) infer the major environmental forces shaping the distribution of a cold-temperate kelp, Laminaria hyperborea (Gunnerus) Foslie, and we (2) predict the effect of past climate changes in shaping regions of long-term persistence (i.e., climatic refugia), where this species might hypothetically harbour higher genetic diversity given the absence of bottlenecks and local extinctions over the long term. We further (3) assessed the consequences of future climate for the fate of L. hyperborea using different scenarios of greenhouse gas emissions (RCP 2.6 and RCP 8.5). Results show NW Iberia, SW Ireland and W English Channel, Faroe Islands and S Iceland, as regions where L. hyperborea may have persisted during past climate extremes until present day. All predictions for the future showed expansions to northern territories coupled with the significant loss of suitable habitats at low latitude range margins, where long-term persistence was inferred (e.g., NW Iberia). This pattern was particularly evident in the most agressive scenario of climate change (RCP 8.5), likely driving major biodiversity loss, changes in ecosystem functioning and the impoverishment of the global gene pool of L. hyperborea. Because no genetic baseline is currently available for this species, our results may represent a first step in informing conservation and mitigation strategies. (C) 2015 Elsevier Ltd. All rights reserved.

2016-02Journal article

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