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Is there plasticity in the cheliped, maxillipeds and gastric mill of Uca formosensis in response to habitat variation?
Author
Ng, Karen Lee Jiun
Supervisor
Lim, Shirley S. L.
Abstract
Uca formosensis is a species endemic to Taiwan. It is found mainly in the muddy habitats on mainland Taiwan; however, a small population was found in the sandy substrates of the Penghu Islands. As Uca species are surface deposit feeders, the substrate of their habitat plays a very important role in their survival. Hence, this study was undertaken to investigate if there was intraspecific variation in the feeding structures of U. formosensis that indicated plasticity in the feeding structures, viz., cheliped, maxillipeds and gastric mill.
The dactyl and propodus length, manus width and cheliped depth of the minor cheliped were measured. The lengths and widths of the first to the third maxillipeds were measured. On the second maxilliped, spoon-tipped setae were counted and examined with a scanning microscope. The width of the median tooth, width of mesocardiac and pterocardiac ossicles, length of the first median tooth ridge, the lengths of all ridges of the median tooth and the length of median tooth and urocardiac ossicle of the gastric mill were measured.
Uca formosensis from the Penghu Islands (sandy habitats) and mainland Taiwan (muddy habitats) was compared with its sympatric species, U. lactea and U. arcuata respectively. This was to ascertain if the feeding structures in U. formosensis were morphologically similar or different from the species that typically inhabit those types of sediments. Similarities with either sympatric species could indicate that the feeding structures of U. formosensis are more suited for that habitat. These phenotypes may be considered as ‘optimal phenotypes’. A feeding structure that does not show a distinct similarity with either sympatric species may be exhibiting an “‘average’ phenotype”.
Within the two populations of U. formosensis, results showed no significant differences in the morphometrics of the chelipeds, maxillipeds and gastric mills, spoontipped setation on the second maxilliped (ANCOVA, P > 0.05) and no differences in the number of ridges on the median tooth in the gastric mill. No plasticity in the feeding structures of U. formosensis was found. Comparisons with a typical sand-inhabiting sympatric species, U. lactea, showed similarities in the cheliped size, second maxilliped length and number of ridges in the median tooth for feeding from sandy substrates, hence, U. formosensis showed ‘optimal phenotypes’ in these structures. Comparisons with a typical mud-inhabiting sympatric species, U. arcuata, showed a similarity in a spoon-tip that was well-developed and serrated. This was the possible ‘optimal phenotype’ for feeding from muddy substrates. “‘Average’ phenotypes” were likely to be the relative size of the third maxilliped and the number of spoon-tipped setae. Even though U. formosensis did not show plasticity in the feeding structures, having a combination of ‘optimal phenotypes’ and “‘average’ phenotypes” may have enabled it to survive in contrasting sediments.
The dactyl and propodus length, manus width and cheliped depth of the minor cheliped were measured. The lengths and widths of the first to the third maxillipeds were measured. On the second maxilliped, spoon-tipped setae were counted and examined with a scanning microscope. The width of the median tooth, width of mesocardiac and pterocardiac ossicles, length of the first median tooth ridge, the lengths of all ridges of the median tooth and the length of median tooth and urocardiac ossicle of the gastric mill were measured.
Uca formosensis from the Penghu Islands (sandy habitats) and mainland Taiwan (muddy habitats) was compared with its sympatric species, U. lactea and U. arcuata respectively. This was to ascertain if the feeding structures in U. formosensis were morphologically similar or different from the species that typically inhabit those types of sediments. Similarities with either sympatric species could indicate that the feeding structures of U. formosensis are more suited for that habitat. These phenotypes may be considered as ‘optimal phenotypes’. A feeding structure that does not show a distinct similarity with either sympatric species may be exhibiting an “‘average’ phenotype”.
Within the two populations of U. formosensis, results showed no significant differences in the morphometrics of the chelipeds, maxillipeds and gastric mills, spoontipped setation on the second maxilliped (ANCOVA, P > 0.05) and no differences in the number of ridges on the median tooth in the gastric mill. No plasticity in the feeding structures of U. formosensis was found. Comparisons with a typical sand-inhabiting sympatric species, U. lactea, showed similarities in the cheliped size, second maxilliped length and number of ridges in the median tooth for feeding from sandy substrates, hence, U. formosensis showed ‘optimal phenotypes’ in these structures. Comparisons with a typical mud-inhabiting sympatric species, U. arcuata, showed a similarity in a spoon-tip that was well-developed and serrated. This was the possible ‘optimal phenotype’ for feeding from muddy substrates. “‘Average’ phenotypes” were likely to be the relative size of the third maxilliped and the number of spoon-tipped setae. Even though U. formosensis did not show plasticity in the feeding structures, having a combination of ‘optimal phenotypes’ and “‘average’ phenotypes” may have enabled it to survive in contrasting sediments.
Date Issued
2013
Call Number
QL444.M33 Ng
Date Submitted
2013