2021 Summer Undergraduate Research Program (SURP) Symposium

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Location

Ballroom, Maucker Student Union, University of Northern Iowa

Presentation Type

Poster Presentation (UNI Access Only)

Document Type

poster

Keywords

Fiddler crabs--Genetics;

Abstract

Populations of a species distributed over great distances are expected to vary in morphology and genetic traits. In fiddler crabs, factors such as substrate, salinity, and larval dispersal can lead to intraspecific variation. Larval dispersal specifically can have a great impact on morphology, as a population with reduced access to dispersion methods will exhibit less morphologic variation. There are six species of fiddler crabs that inhabit the western Atlantic coast between the Tropic of Cancer and the Tropic of Capricorn. In order to determine the degree of variation between and within species that inhabit this region, we performed geometric morphometric analysis on two of the four species that have not been analyzed for variation. We hypothesized that the two species would be morphologically distinct, but that the currents that distribute larvae would have an effect on the variation within the species. To examine geographic variation in fiddler crabs, we photographed and digitized 272 Minuca mordax (Smith 1870) from 17 localities and 201 Leptuca leptodactyla (Rathbun 1898) from 15 localities. The analysis used 23 fixed landmarks to describe shape. The two species were found to be significantly different in carapace shape. The carapace shape of M. mordax varies geographically. Specimens from northern and southern Brazil are more similar in shape to each other than those from Central America. When analyzed for allometric growth, M. mordax shows little shape variation in relation to size. On the other hand, carapace shape in L. leptodactyla exhibits little regionalization. However, unlike M. mordax, in this species regression analysis suggests that allometric variation has a greater impact on shape, but it still remains below 10%. The pattern of variation in M. mordax supports the hypothesis that species with limited larval distribution and a large geographic range can exhibit significant differences among populations. Analysis of L. leptodactyla demonstrates that a species with a large range and greater larval dispersal potential may not show regionalization. Consequently variation is inversely related to dispersal potential.

Start Date

30-7-2021 11:30 AM

End Date

30-7-2021 1:15 PM

Event Host

Summer Undergraduate Research Program, University of Northern Iowa

Faculty Advisor

Carl L. Thurman

Department

Department of Biology

Creative Commons License

Creative Commons Attribution-NonCommercial 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License

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Jul 30th, 11:30 AM Jul 30th, 1:15 PM

Geometric Morphometric Analysis of Fiddler Crabs from the Shore of the Western Atlantic Ocean

Ballroom, Maucker Student Union, University of Northern Iowa

Populations of a species distributed over great distances are expected to vary in morphology and genetic traits. In fiddler crabs, factors such as substrate, salinity, and larval dispersal can lead to intraspecific variation. Larval dispersal specifically can have a great impact on morphology, as a population with reduced access to dispersion methods will exhibit less morphologic variation. There are six species of fiddler crabs that inhabit the western Atlantic coast between the Tropic of Cancer and the Tropic of Capricorn. In order to determine the degree of variation between and within species that inhabit this region, we performed geometric morphometric analysis on two of the four species that have not been analyzed for variation. We hypothesized that the two species would be morphologically distinct, but that the currents that distribute larvae would have an effect on the variation within the species. To examine geographic variation in fiddler crabs, we photographed and digitized 272 Minuca mordax (Smith 1870) from 17 localities and 201 Leptuca leptodactyla (Rathbun 1898) from 15 localities. The analysis used 23 fixed landmarks to describe shape. The two species were found to be significantly different in carapace shape. The carapace shape of M. mordax varies geographically. Specimens from northern and southern Brazil are more similar in shape to each other than those from Central America. When analyzed for allometric growth, M. mordax shows little shape variation in relation to size. On the other hand, carapace shape in L. leptodactyla exhibits little regionalization. However, unlike M. mordax, in this species regression analysis suggests that allometric variation has a greater impact on shape, but it still remains below 10%. The pattern of variation in M. mordax supports the hypothesis that species with limited larval distribution and a large geographic range can exhibit significant differences among populations. Analysis of L. leptodactyla demonstrates that a species with a large range and greater larval dispersal potential may not show regionalization. Consequently variation is inversely related to dispersal potential.