Zoological Studies 44(2): 242-251 (2005) Chimney Building by Male Uca formosensis Rathbun, 1921 (Crustacea: Decapoda: Ocypodidae) after Pairing: A New Hypothesis for Chimney Function Hsi-Te Shih1,2,*, Hin-Kiu Mok2, and Hsueh-Wen Chang3 1Department of Life Science, National Chung-Hsing University, Taichung, Taiwan 402, R.O.C. Tel/Fax: 886-4-22856496. E-mail: [email protected] 2Institute of Marine Biology, National Sun Yat-sen University, Kaohsiung, Taiwan 804, R.O.C. 3Department of Biological Sciences, National Sun Yat-sen University, Kaohsiung, Taiwan 804, R.O.C. (Accepted February 8, 2005) Hsi-Te Shih, Hin-Kiu Mok, and Hsueh-Wen Chang (2005) Chimney building by male Uca formosensis Rathbun, 1921 (Crustacea: Decapoda: Ocypodidae) after pairing: a new hypothesis for chimney function. Zoological Studies 44(2): 242-251. The construction of a chimney after pairing is first described for Uca for- mosensis Rathbun, 1921, a fiddler crab endemic to Taiwan. After attracting a female into his burrow, the male builds a chimney averaging 9.2 cm high and 7.7 cm in diameter at the base within a 4- or 5-d period before the next neap tide. It is not related to sexual attraction because the chimney does not appear prior to or during courtship. To build the chimney, the male excavates the burrow which probably widens the shaft and, more importantly, deepens the burrow so that it reaches the water table, thus providing a moist chamber in which the female can incubate her eggs. The mudballs dug out from within the burrow are piled around the entrance and form the chimney, which herein is assumed to function as a way for the builder to hide from its enemies. The sex ratio of U. formosensis present on the surface was also recorded and is discussed. http://www.sinica.edu.tw/zool/zoolstud/44.2/242.pdf Key words: Fiddler crabs, Behavior, Underground mating, Mudflats, Taiwan. Some crabs (and other crustaceans) build 1984), and igloos (Dotilla: Takeda et al. 1996). structures (pillars, hoods, chimneys, etc.) next to Crane (1975) reviewed these structures in fiddler their burrows (Powers and Bliss 1983). Some of crabs of the world, and chimneys were found in these structures have been shown to function for some subgenera: Deltuca (U. dussumieri, U. arcu- sexual attraction, e.g., pillars (Uca: Christy 1988a ata, U. forcipata, U. coarctata, and U. urvillei), b), hoods (Uca: Zucker 1974 1981, Christy et al. Thalassuca (U. tetragonon), Amphiuca (U. 2002 2003), mudballs (Uca: Oliveira et al. 1998), chlorophthalmus), Boboruca (U. thayeri), Minuca and pyramids (Ocypode: Linsenmair 1967, Hughes (U. vocator), and Celuca (U. cumulanta and U. 1973); some are related to disturbance (fighting or stenodactylus). Other fiddler species were also burrow occupation) caused by neighbors, e.g., reported to build chimneys, e.g., U. elegans of the hoods (Uca: Zucker 1974 and Cleistostoma: subgenus Australuca (George and Jones 1982) Clayton 1988), chimneys (Uca: Salmon 1987, and U. subcylindrica of the subgenus Minuca Wada and Murata 2000), and barricades (Ilyoplax: (Thurman 1984) (reviewed in Table 1). Wada 1984); and some are related to environmen- Uca formosensis Rathbun, 1921 is a species tal regulation, e.g., hoods (Uca: Powers and Cole of fiddler crab endemic to Taiwan. This species is 1976), chimneys (Uca: Crane 1975: 524, Thurman poorly known except for its morphological charac- * To whom correspondence and reprint requests should be addressed. 242 Shih et al. -- Chimney Building by Uca formosensis 243 ters (see Shih et al. 1999). From preliminary Uca formosensis is distributed on the west observations, many large chimneys were periodi- coast of Taiwan, including the Penghu Archipelago cally found in the habitat of U. formosensis. The (the Pescadores) (Shih et al. 1999). From 7 to 21 chimneys of this species have not been described July 1996, successive observations on chimney in detail before (Shih et al. 1999). In this paper, we building were conducted in Shengang, Changhua describe results based on successive observations County. Two plots (2 x 2 m) were selected in , in Changhua, west-central Taiwan, and on data which to monitor the crabs behavior. From 08:00 recorded on mudflats along the western coast of to 18:00, numbers of males and females in each Taiwan. A chimney of U. formosensis is built by plot and 3 temperature readings were recorded the male of a pair after he has attracted a female each hour, except for the period when the habitat into his burrow for underground mating, and it was covered by water at high tide. The 3 tempera- therefore is not a courtship signal. The function of tures recorded were the ground temperature in chimney building is proposed and discussed in this sunshine (sun temperature), ground temperature study. The chimneys built by U. arcuata (de Haan, under the shade of some object (shade tempera- 1835) are also recorded for comparison. In addi- ture), and soil temperature at a depth of about 12 tion, we also recorded and discuss the sex ratio of cm by inserting the probe of a Digital Thermo U. formosensis present on the surface. (Digital Taschen-Thermometer). The sex ratio, males/females, appearing on these plots was also , calculated each hour. One hour s data in 21 July MATERIALS AND METHODS are not included as sex ratio was 16:0. The process of chimney building and other Table 1. A summary of chimneys built around burrow entrances by Uca fiddler crabs Species Subgenus defined Materials Builder References by Crane (1975) U. formosensis ?a from within the burrow mostly male and this study seldom female U. arcuata Deltuca mostly from the surface both sexes Crane 1975, Yeh 1996, Wada and Murata 2000 U. coarctata Deltuca both sexes Crane 1975 U. coarctata flammula Deltuca Crane 1975 U. dussumieri Deltuca both sexes Crane 1975 U. paradussumieri Deltuca Ng and Sivasothi 1999 U. forcipata Deltuca from within the burrow female Crane 1975 U. urvillei Deltuca from within the burrow male (?) and female Crane 1975 U. elegans Australuca George and Jones 1982 U. tetragonon Thalassuca from the surface female Crane 1975 U. chlorophthalmus Amphiuca female Crane 1975 crassipes U. chlorophthalmus Amphiuca female Crane 1975 U. thayeri Boboruca from the surface (?) female von Hagen 1970, Crane 1975, Salmon 1987, Kellmeyer and Salmon 2001, Weaver and Salmon 2002 U. galapagensis Minuca male von Hagen 1968 U. minax Minuca Montague 1980 U. pugnax Minuca Montague 1980 U. subcylindrica Minuca from within the burrow (?) Thurman 1984 U. vocator Minuca both sexes Crane 1975 U. cumulanta Celuca Crane 1975 U. stenodactylus Celuca female (?) Crane 1975 aBased on Shih et al. (1999). 244 Zoological Studies 44(2): 242-251 (2005) related behaviors were recorded on video tape. Twelve females were observed to excavate Reproductive behaviors (e.g., courtship, surface mudballs from within the burrow and five of these mating, underground mating, etc.) and other females were ovigerous. The female piled up the behaviors (e.g., fighting, feeding, etc.) were mudballs loosely beside, but not around, the bur- recorded by ad libitum sampling (Martin and row, and the resulting structure resembled a pyra- , Bateson 1993). If a certain behavior pattern was mid (Fig. 1H), not a cylinder like the male s chim- observed, it was recorded until it ceased. Some ney. burrows with chimneys were dug out, and the sex and carapace width (CW) of the pair were mea- Chimney building sured, as well as the reproductive condition of the female. The depth of the burrow and its relative We determined the process and timing of distance to the high tide mark were also recorded. chimney building from successive 15 d observa- Behaviors related to chimney building in Jhuwei tions conducted in Shengang, Changhua, Taiwan. (Taipei County), Jinshuei (Hsinchu City), 1. During the period of a neap tide, the Haishangu (Hsinchu City), Shengang (Changhua amount of time that the tide covered the habitat of Co.), Dongshih (Chiayi Co.), Budai (Chiayi Co.), U. formosensis (in the high intertidal zone) and Cigu (Tainan Co.) from Sept. 1994 to Apr. decreased each day. About 1 or 2 d before the 1997 were also recorded to supplement the tide did not cover its habitat, males began courting results. wandering females. When a female stayed inside Uca arcuata (de Haan) is another species in his burrow, the male began to build a chimney. Taiwan that frequently builds chimneys. Its chim- The male excavated mudballs from inside the bur- ney building behavior was also recorded and is row, carrying them using its ambulatories on the described for comparison. minor side (Fig. 1G), and piled them on one side of the burrow entrance. The crab did not place mud- balls on the other side until the chimney was fin- RESULTS ished. Therefore, the structure appeared hood- shaped while it was being built (Fig. 1B, G). The Chimneys of U. formosensis appeared on the original entrance was plugged by mudballs to 3~5 mudflats of the high intertidal zone during the peri- cm in depth (Fig. 1E), while the entrance of the od of the neap tide in the warm season (Mar. to chimney sometimes became plugged by 1 or 2 Oct.) in Taiwan (Fig. 1A). mudballs (Fig. 1F). Meanwhile, the female stayed inside the burrow, and it was assumed that she did Chimney structure not participate in the building process. A chimney could be finished in 1 d. After a male U. formosensis had attracted a 2. On the day the tide first failed to cover the female to stay inside his burrow for underground habitat (e.g., during the day on 10 July, Fig. 2C), mating, the male began to build a tower-like cylin- most chimneys had already been built.