Searching for evidence of local adaptation in Sea Rocket (Cakile maritima Scop.)

Abstract

Exploring the ecological and evolutionary processes that shape species is at the heart of evolutionary ecology. Phenotypic variation influences a species’ interactions with its environment, comes under direct selection, and has numerous ecological effects. Analysing the nature of intraspecific variation and local adaptation, and gaining a better understanding of how they are formed and maintained by eco-evolutionary dynamics, is key in predicting and elucidating the response of populations and ecosystems to environmental change. This thesis sets outs our search for evidence of local adaptation in Cakile maritima Scop., the European Sea Rocket. Our central aims were to establish whether local adaptation is a feature of the system and whether environmental conditions might be driving adaptation in Sea Rocket. We quantified and analysed variation in fruit and seed traits relating to dispersal and establishment, floral traits, and leaf morphology between populations across Great Britain and the Baltic, and explored the patterns of this variation in an environmental context. Analysis of bioclimatic variables revealed patterns of environmental heterogeneity between our sample populations and across the native range, highlighting gradients in temperature variables and annual precipitation from west to east across this subregion. Significant between-population variation was observed in fruit and seed traits, with fruits and seeds becoming lighter and smaller with a move eastwards across the region of study which correlated with changes in bioclimatic variables and a gradient in seawater salinity. Significant variation in the timing of flowering and petal colour was also observed; plants flowered earlier and after producing a greater number of leaves, and petal colour became darker, towards the east. Finally, significant between-population variation was found in leaf morphology, with a gradient from shorter, more entire leaves in the west to elongated and highly lobed leaves in the east of the region of study. The relationship between leaf shape and environmental variables suggested that variation in precipitation and temperatures could be shaping the observed gradient in leaf shape in Sea Rocket. Our findings suggest that local adaptation is likely a feature of this system and that spatial heterogeneity of environment may be shaping adaptations to local conditions. This research greatly improves the understanding of intraspecific variation in Cakile maritima and provides new insights into trait-environment relationships. Our research highlights that Sea Rocket merits further development as a model species, and lays the groundwork for future studies using this species to deepen our knowledge of the ecological and evolutionary processes that shape species.

Date of Award	4 Nov 2020
Original language	English
Awarding Institution	University of Bath
Supervisor	Paula Kover (Supervisor) & Roderick Scott (Supervisor)