Chinese

Systematics of Uca formosensis Rathbun, 1921 (Crustacea: Decapoda: Ocypodidae), an Endemic Fiddler Crab from Taiwan, based on Morphological, Genetic and Ecological Evidence

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Hsi-Te Shih

(Advisors: Drs. Hin-Kiu Mok, Hsueh-Wen Chang and Sin-Che Lee)

Institute of Marine Biology, National Sun Yat-sen University, Kaohsiung 804, Taiwan

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        Uca formosensis Rathbun, 1921 is an endemic fiddler crab from Taiwan. The taxonomy of this species has long been constrained by the paucity of specimens in major museums. It is necessary to conserve this species by understanding its natural history as most of its habitat are under threat. The aim of this study was to investigate the systematics of the species using morphological, biochemical, behavioral and ecological approaches. Females generally have an enlarged tooth on each finger of the minor chelipeds. In contrast, males lack teeth on both fingers of the minor chelipeds. The ratio of handedness of chelipeds is the same (50 : 50) for males. Variation on the anterolateral margins of the carapace, suborbital margin, orbital floor and the living coloration were also studied. Results from characters such as handedness, presence of enlarged teeth on the fingers of the female's minor chela, structures of the anterolateral margin, suborbital margin, orbital floor, degree of arching of the carapace and habitat preference suggest that U. formosensis is different from the other members of the subgenus Thalassuca (U. tetragonon and U. vocans). Population genetics of U. formosensis from six sites were compared by allozyme analysis. The average genetic differentiation coefficient (FST) was 0.030, implying that there was little genetic differentiation among the crabs from various sites. The average genetic distance (D) among populations was as low as 0.0015. However, the genetic distance between Chiku population and all other populations was much higher. Since Chiku habitat was an isolated fish pond, the differentiation is probably caused by the low gene flow with other sites and the founder effect. Some allele frequencies of the populations from mangrove habitats of Chuwei and Tungshih were different from the rest of populations. The genetic distance from allozyme analysis indicated that U. formosensis was close to the subgenus Deltuca. U. formosensis is therefore suggested to be placed in the subgenus Deltuca. The results of the behavioral study indicate that U. formosensis posses two types of mating system: surface mating and underground mating. In surface mating, males tried to approach those neighboring females having their own burrows without exhibiting courtship behavior. Mating sites were the surface near the burrow of females. After the mating, the participants returned to their own burrows. Feeding continued after mating. In underground mating, the male vigorously waved the major cheliped to attract the wandering female and directed approaching female to his burrow with his carapace facing toward her (the back-pushing behavior). When a female went into a male's burrow, male followed her immediately, which is a "female-first" type of courtship. Some males displayed a bout of shivering behavior with their major chelipeds before they followed the females into the burrows. Underground mating males were larger than the females, but there was no significant correlation between the size of the pairs. After successfully attracting the female into his burrow, the male would build a large chimney in face of the drought period before next of the coming neap tide. The construction of chimney after pairing is first reported in the present study. It is not related to sexual attraction. Chimney was not for sunshading or ventilation because its entrance was plugged and the burrow bottom was not located just below the entrance. Chimney provides a moist burrow for the ovigerous female to hatch her eggs. Usually the male dug a large and deep burrow reaching the water table to accommodate the pair. The pellets dug out were conveniently put beside the entrance without any special purpose. Piling up of the substrate to chimney shape was likely to prevent the builder from its enemies. From the survey undertaken between 1994 to 1997, U. formosensis was only found in Taiwan and Penghu. Its zoogeographical distribution was limited and scattered, because most habitats were threatened by development. Habitats with large population of U. formosensis were usually open and less sheltered shores with gray clayey mud, e.g., Haishanku, Shenkang and Chiku; while small population occurred in those habitats with dense mangrove, e.g., Chuwei, Chinshui, Fangyuan, Tungshih and Chinglo.

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Contents

ABSTRACT
I. Introduction
II. Historic reviews on Uca formosensis
III. Materials and methods
    1. Study sites
    2. General methods
    3. Morphological analysis
    4. SEM micrographs of gonopod and gonopore
    5. Analysis of allozyme electrophoresis
        Statistical analysis
    6. Mating systems
        1) Recording of reproduction behaviors
            Sampling and recording rules for behavioral study
        2) Chimney building beside burrow entrance
IV. Morphology of Uca formosensis
    1. Results
        1) Handedness and chela type
        2) Allometric growth of carapace width versus propodus length of major cheliped
        3) Cladistic relationships among Uca formosensis, U. arcuata, U. vocans borealis and U. lactea lactea
    2. Discussion
        1) Validity of Uca formosensis belonging in the subgenus Thalassuca Crane, 1975
            (1) Handedness
            (2) Minor cheliped gape of female
            (3) Anterolateral margin
            (4) Suborbital margin and orbital floor
            (5) Carapace and habitat
        2) Updating Crane (1975)
        3) Allometric growth of carapace and major cheliped
V. Genetic differences among four species of Taiwanese fiddler crabs and genetic structure of populations of Uca formosensis
    1. Results
        1) Allozyme analysis
        2) Genetic differences among Uca formosensis, U. arcuata, U. vocans borealis and U. lactea lactea
        3) Genetic structure among populations of Uca formosensis
    2. Discussion
VI. Mating system of Uca formosensis
    1. Results
        1) Surface mating of Uca formosensis
        2) Underground mating of Uca formosensis
        3) Vertical waving behavior of male
        4) Shivering behavior of the major cheliped of male
        5) Unusual reproductive behaviors
    2. Discussion
        1) A review of the studies of two types of mating systems of fiddler crabs
            (1) Stage 1: initial stage
            (2) Stage 2: dichotomy stage
            (3) Stage 3: suspicion stage
            (4) Stage 4: coexist stage
        2) Proximate causes for the two types of mating systems
        3) Evolutionary relationship between two types of mating system
        4) Waving behavior of the male
        5) Shivering behavior of the major cheliped of the male
        6) Mating of the male and the ovigerous female
VII. Chimney building of Uca formosensis
    1. Results
        1) Description of the chimney
        2) General process of chimney building related to tide rhythm
        3) Relationship between the reproductive condition of female and chimney
    2. Discussion
        1) Function of the chimney of Uca formosensis
            (1) Sexual attraction hypothesis
            (2) Sunshading effect hypothesis
            (3) Ventilation hypothesis
            (4) Keeping off intruder hypothesis
            (5) Hiding effect hypothesis
        2) Chimney of female Uca formosensis
        3) Relative vertical location inside the burrow between the pair of Uca formosensis
VIII. Ecological studies on Uca formosensis
    Results and Discussion
        1) Distribution of Uca formosensis
        2) Some characteristics of the habitats of Uca formosensis
            (1) Vegetation of habitat
            (2) Other sympatric crustaceans
        3) Pressure of predation of Uca formosensis
        4) Change of habitat of Uca formosensis
            (1) Negative impact of mangrove
            (2) Damage caused by typhoons
        5) Damages of Uca formosensis made by human
            (1) Capture
            (2) Pressure of development
        6) Suggestion for the conservation of Uca formosensis
IX. Conclusion
X. Summary
Literature cited
Acknowledgments
Appendix I. The Chinese localities used in the text with the Romanization spelling
Appendix II. The Chinese and Japanese names used in the text with the Romanization spelling

Copyright © 2005 Hsi-Te Shih