Browsing by Author "McQuaid, C. D."
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- Coastal topography drives genetic structure in marine musselsPublication . Nicastro, Katy; Zardi, Gerardo; McQuaid, C. D.; Teske, P. R.; Barker, N. P.Understanding population connectivity is fundamental] to ecology, and, for sedentary organisms, connectivity is achieved through larval dispersal. We tested whether coastal topography influences genetic structure in Perna Perna mussels by comparing populations inside bays and on the open coast. Higher hydrodynamic stress on the open coast produces higher mortality and thus genetic turnover. Populations on the open coast had fewer private haplotypes and less genetic endemism than those inside bays. Gene flow analysis showed that bays act as Source populations, with greater migration rates Out. of bays than into them. Differences in genetic structure on scales of 10s of kilometres show that coastal configuration strongly affects selection, larval dispersal and haplotype diversity,
- Comparison of phototrophic shell-degrading endoliths in invasive and native populations of the intertidal mussel Mytilus galloprovincialisPublication . Marquet, Nathalie; Nicastro, Katy R; Gektidis, M.; McQuaid, C. D.; Pearson, G. A.; Serrão, Ester; I Zardi, GerardoThe intertidal mussel Mytilus galloprovincialis is a successful invader worldwide. Since its accidental introduction onto the South African west coast in the late 1970s, it has become the most successful marine invasive species in South Africa. One possible explanation for this phenomenon is that M. galloprovincialis suffers less from phototrophic shell-degrading endoliths in its invasive than in its native range. We assessed photoautotrophic endolithic pressure on M. galloprovincialis in native (Portugal) and invasive (South Africa) ranges. Invasive populations were more heavily infested than native populations. In Portugal, only the biggest/oldest mussels displayed endolithic erosion of the shell and the incidence of infestation was greater at higher shore levels where more prolonged exposure to light enhances endolith photosynthesis. In South Africa, even the smallest size classes of mussels were heavily infested throughout the shore. In Portugal, endolithicinduced mortality was observed at only one location, while in South Africa it occurred at all locations and at significantly higher rates than in Portugal. Important sub-lethal effects were detected in infested native mussels, confirming previous studies of invasive populations and suggesting an energy trade-off between shell repair and other physiological constraints. We observed a positive relationship between infestation rates and barnacle colonization on mussel shells, suggesting possible facilitation of barnacle settlement/survival by shell-boring pathogens. Identification of endoliths revealed common species between regions. However, two species were unique in the invasive range while another was unique in the native region. Different levels of endolithic infestation in the invasive and the native range were not explained by the effect of major environmental determinants (Photosynthetically Available Radiation and wave height). The results reject our initial hypothesis, indicating that invasion success of M. galloprovincialis is not simply explained by escape from its natural enemies but results from complex interactions between characteristics of the invaded community and properties of the invader.
- Enemies with benefits: parasitic endoliths protect mussels against heat stressPublication . Zardi, Gerardo I.; Nicastro, Katy R; McQuaid, C. D.; Ng, T. P. T.; Lathlean, J.; Seuront, L.Positive and negative aspects of species interactions can be context dependant and strongly affected by environmental conditions. We tested the hypothesis that, during periods of intense heat stress, parasitic phototrophic endoliths that fatally degrade mollusc shells can benefit their mussel hosts. Endolithic infestation significantly reduced body temperatures of sun-exposed mussels and, during unusually extreme heat stress, parasitised individuals suffered lower mortality rates than nonparasitised hosts. This beneficial effect was related to the white discolouration caused by the excavation activity of endoliths. Under climate warming, species relationships may be drastically realigned and conditional benefits of phototrophic endolithic parasites may become more important than the costs of infestation.
- Intraspecific genetic lineages of a marine mussel show behavioural divergence and spatial segregation over a tropical/subtropical biogeographic transitionPublication . Zardi, Gerardo I.; Nicastro, Katy R; McQuaid, C. D.; Castilho, Rita; Costa, Joana; Serrão, Ester; Pearson, G. A.Background: Intraspecific variability is seen as a central component of biodiversity. We investigated genetic differentiation, contemporary patterns of demographic connectivity and intraspecific variation of adaptive behavioural traits in two lineages of an intertidal mussel (Perna perna) across a tropical/subtropical biogeographic transition. Results: Microsatellite analyses revealed clear genetic differentiation between western (temperate) and eastern (subtropical/tropical) populations, confirming divergence previously detected with mitochondrial (COI) and nuclear (ITS) markers. Gene flow between regions was predominantly east-to-west and was only moderate, with higher heterozygote deficiency where the two lineages co-occur. This can be explained by differential selection and/or oceanographic dynamics acting as a barrier to larval dispersal. Common garden experiments showed that gaping (periodic closure and opening of the shell) and attachment to the substratum differed significantly between the two lineages. Western individuals gaped more and attached less strongly to the substratum than eastern ones. Conclusions: These behavioural differences are consistent with the geographic and intertidal distributions of each lineage along sharp environmental clines, indicating their strong adaptive significance. We highlight the functional role of diversity below the species level in evolutionary trends and the need to understand this when predicting biodiversity responses to environmental change.
- Love thy neighbour: group properties of gaping behaviour in mussel aggregationsPublication . Nicastro, Katy R; I Zardi, Gerardo; McQuaid, C. D.; Pearson, G. A.; Serrão, EsterBy associating closely with others to form a group, an animal can benefit from a number of advantages including reduced risk of predation, amelioration of environmental conditions, and increased reproductive success, but at the price of reduced resources. Although made up of individual members, an aggregation often displays novel effects that do not manifest at the level of the individual organism. Here we show that very simple behaviour in intertidal mussels shows new effects in dense aggregations but not in isolated individuals. Perna perna and Mytilus galloprovincialis are gaping (periodic valve movement during emersion) and non-gaping mussels respectively. P. perna gaping behaviour had no effect on body temperatures of isolated individuals, while it led to increased humidity and decreased temperatures in dense groups (beds). Gaping resulted in cooler body temperatures for P. perna than M. galloprovincialis when in aggregations, while solitary individuals exhibited the highest temperatures. Gradients of increasing body temperature were detected from the center to edges of beds, but M. galloprovincialis at the edge had the same temperature as isolated individuals. Furthermore, a field study showed that during periods of severe heat stress, mortality rates of mussels within beds of the gaping P. perna were lower than those of isolated individuals or within beds of M. galloprovincialis, highlighting the determinant role of gaping on fitness and group functioning. We demonstrate that new effects of very simple individual behaviour lead to amelioration of abiotic conditions at the aggregation level and that these effects increase mussel resistance to thermal stress.
- Movement behaviour and mortality in invasive and indigenous mussels: resilience and resistance strategies at different spatial scalesPublication . Nicastro, Katy; Zardi, Gerardo; McQuaid, C. D.The responses of indigenous and exotic species to environmental factors can differ across spatial and temporal scales, and it is this difference that determines invasion success and the dynamics of co-existence, In South Africa, the indigenous Perna perna and the invasive Mytilus galloprovincialis are the dominant intertidal mussels on the southern coast, where they co-exist. We compared their movement behaviour over 6 mo at small scales (within and at the edge of mussel beds) and at meso scales (in bays and on the open coast). M, galloprovincialis moved more and had higher mortality rates than did P. perna. For both species, mortality was greater at the edge than at the centre of beds, and on the open coast than in bays. Mussels at the edge of beds moved more than those within beds, but, while this was true for M. galloprovincialis in both habitats, P. perna did not show a position effect on the open coast. Cross-correlation analysis showed that movement rates of both species were correlated with mortality rates after a lag of 1. mo. These results suggest that following mortality events, mussels react to increased availability of space and decreased attachment to neighbours by increasing their movement to reorganise into a safer arrangement. However, P. perna and M. galloprovincialis effectively adopt resistance and resilience strategies, respectively. The effectiveness of each strategy depends on environmental conditions in different habitats, influencing the possibility of co-existence. The higher hydrodynamic stresses experienced in open coast habitats and at the edge of a mussel bed are disadvantageous to the more active, less strongly attached invasive species.