Spatially varying selection on shell color phenotype in the flat periwinkle Littorina obtusata / Megan V. Phifer-Rixey.

Format:

Book

Manuscript

Thesis/Dissertation

Author/Creator:

Phifer-Rixey, Megan V.

Contributor:

Schmidt, Paul, advisor.

University of Pennsylvania.

Language:

English

Subjects (All):

Penn dissertations--Biology.

Biology--Penn dissertations.

Local Subjects:

Penn dissertations--Biology.

Biology--Penn dissertations.

Physical Description:

xv, 279 pages : illustrations ; 29 cm

Production:

2009.

Summary:

Clinal patterns of shell color morph frequencies in the intertidal snail Littorina obtusata present a unique opportunity to explore the effects of variable thermal regime in an ecologically important system. L. obtusata are found in the mid-intertidal region of rocky shores in the northern Atlantic. Temperature and desiccation are well documented as the primary abiotic determinants of distributional patterns in such habitats making them an ideal context for investigation. Further, shell color is predicted to affect response to thermal regime; dark animals are expected to absorb more visible light than lighter animals. We hypothesized that shell color in L. obtusata is under selection via thermal regime and that variation in thermal regime contributes to patterns of shell color morph frequencies across the Gulf of Maine. We found that: (1) Frequencies of shell color variants varied predictably with thermal regime and exhibited pronounced clines at multiple spatial scales. Lighter snails increased in frequency with increasing heat/desiccation stress, while darker snails decreased in frequency. Patterns of differential survivorship under episodic high temperatures were consistent with observed clines. Using a manipulative approach, shell color was shown to directly affect survivorship under such conditions. (2) Analysis of microsatellite variation suggests that populations of L. obtusata in the Gulf of Maine are connected by migration. Additionally, patterns of shell color morph frequencies contrast with variation at microsatellite loci indicating the action of selection on shell color rather than neutral processes alone. (3) Shell color has subtle effects on growth and strong effects on behavior. At spatial scales that reflect behavioral response, light snails were more likely to be found in hotter areas with more desiccation risk and the differences in distribution between color morphs were dependent on environmental conditions. (4) There is considerable morphological variation in Littorina obtusata within the Gulf of Maine. In addition to variation in shell color, there were striking trends in variation in shell patterning and body pigmentation, possibly indicating the action of selection.

Taken together, these results provide a compelling example of natural selection and of the potential for variation in thermal regime to affect the evolution of natural populations.

Notes:

Adviser: Paul Schmidt.

Thesis (Ph.D. in Biology) -- University of Pennsylvania, 2009.

Includes bibliographical references.

OCLC:

615808401