Chang-Po Chen

Nucleotide Sequences of Ribosomal Internal Transcribed Spacers and Their Utility in Distinguishing Closely Related Perinereis Polychaets (Annelida; Polychaeta; Nereididae)

Abstract: Nucleotide sequences of a segment of the rRNA transcription unit spanning from the 3′ end of the 18S rDNA to the 5′ end of 28S rDNA were determined for four species of Perinereis polychaetes: P. aibuhitensis, P. floridana, and two undescribed species, Perinereis sp1 and sp2. The 5.8S rDNA sequences are identical among the four species. Intraspecific variability was low with the Kimura 2-parameter (K2P) distance, ranging from 0 to 0.0138 for ITS1 and 0 to 0.0247 for ITS2. The interspecific nucleotide difference was significantly higher than those within species, with a mean K2P of 0.172 for ITS1 and 0.204 for ITS2, suggesting that comparisons of ITS regions can be used to evaluate the phylogenetic relationships among Perinereis species. Both neighbor-joining and parsimony analyses of ITS variability indicate a close relationship between the two undescribed species of Perinereis. These findings highlight the utility of the ITS sequence in conjunction with other morphological and ecological characters to delineate species boundaries among closely related polychaetes.

Mating behaviour and reproductive cycle of Archaster typicus (Echinodermata: Asteroidea)

This study examines the reproductive cycle, the mechanism of male-on-female pairing behavior and the spawning behavior of Archaster typicus Müller et Troschel. Field studies were conducted in the intertidal zone of the sand beaches at Penghu, Taiwan (23 32′N; 119 33′E) at ebb-tide in 1984 and 1985. The pairing behavior of A. typicus is a reproductive behavior which leads to simultaneous spawning, increasing the probability of fertilization. As the breeding season approaches, sea stars, especially males, display increased mobility. Because only males tend to mount another individual and because males can detect the sex of another individual by contact with the side of their arms, a male-on-female pair is formed when a male encounters a female. Eighty-five percent of the sea stars observed were paired during the pairing season. Spawning by a paired female is closely followed by spawning of its paired male; male spawning, however, does not induce spawning in its paired female. During spawning, the male turns slightly so that its arms overlap the arched arms of the female. The gonad volume of males is much less than that of females. This may result from the high efficiency of fertilization in this species, which does not require a large amount of gametes to be released, or from the higher energetic demands made on the males.

Reproductive cycles of tropical sea cucumbers (Echinodermata: Holothuroidea) in southern Taiwan

Reproductive cycles of Afrocucumis africana (Dendrochirotida), Actinopyga echinites, Holothuria leucospilota, H. cinerascens, H. difficilis (Aspidochirotida), Synaptamaculata, Opheodesoma grisea, Patinapta taiwaniensis and Polycheira rufescens (Apodida), representing three orders of intertidal holothurians in southern Taiwan, were determined by gonad index and histological examination from March 1990 through September 1991. All nine species of holothurians have annual spawning periods lasting 2 to 4 mo in spring or summer. The early spawning of H. cinerascens and P. rufescens (suspension feeders) suggests that their feeding mode is related to food resources and may influence the reproductive period. In the direct-developing dendrochirotid (suspension feeder), gonad development occurs in cool months, and gametes are released at the beginning of warm months. In indirect-developing aspidochirotid and apodid (deposit feeder), gamete release occurs in late spring or summer and appears to be correlated with summer phytoplankton growth. The holothurians in the present study display spawning periodicity and duration similar to those of temperate species. Four species of holothurians lengthened spawning season with decreased latitude.

Reproduction and growth of Holothuria atra (Echinodermata: Holothuroidea) at two contrasting sites in southern Taiwan

AbstractReproductive periods and growth of two populations of Holothuria atra Jaeger distinctly different in body size at two sites of southern Taiwan were determined. Individuals examined in the present study were collected between march 1990 and February 1992. At Nanwan (21° 57′N, 120° 45′E), large individuals (351 to 1400 g wet wt) spawned from June to September. At Wanlitung (22°N, 120° 42′E), a small proportion of frequently dividing individuals (<190 g wet wt) have mature gonads in May, June and September, but histological examination revealed no sign of spawning. Sexual recruits, defined as small individuals <5 g wet wt without sign of regeneration, were not found at either site during this 2-yr study. After the peak of fission at Wanlitung, 40% of the population showed signs of external regeneration. At Nanwan, small individuals transferred from Wanlitung grew from 6 g (n=6) to 166±8 g

Reproductive cycle, larval development, juvenile growth and population dynamics of Patiriella pseudoexigua (Echinodermata: Asteroidea) in Taiwan

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Comparison of larval development and growth of the sea cucumberActinopyga echinites: Ovary-induced ova and DTT-induced ova

within 8 mo, and from 48±4 g (n=50) to 324±16 g within 1 yr, with a 6.8-fold biomass increase in 1 yr. At Wanlitung, the monthly average body weight of H. atra is between 33 and 62 g, apparently due to frequent fission, and the biomass increased only 2.9-fold in 1 yr. In southern Taiwan, sexual reproduction of H. atra occurs in large individuals. Asexual reproduction, occurring in small individuals, is the chief mechanism for population maintenance and increase, but it may decrease sexual reproductive potential.

Larval Growth of the Coconut Crab Birgus Latro with a Discussion on the Development Mode of Terrestrial Hermit Crabs

Populations of Holothuria atra Jaeger occurring at Wanlitung and Nanwan were sampled monthly at spring tide from March 1990 to February 1992 in southern Taiwan. At Wanlitung, small individuals with evidence of fission and regeneration were abundant in shallow tidepools on the wide reef flats (density: 98±40 ( ± SD) 100 m-2, body weight: 6 to 182 g). At Nanwan, large individuals with no evidence of fission were sparse in deep tidepools and narrow flats [density: 0.24±0.07 ( ± SD) 100 m-2, body weight: 351 to 1400 g]. At Wanlitung, fission occurred throughout the year with an average monthly fission frequency of 4.5%, peaking at 18% in September 1990 and 16% in August 1991. Fission was accomplished by revolving, twisting, and stretching of the body, resulting in two unequal fragments. The minimal weight of 3007 individuals measured during 1 yr at Wanlitung was 6 g. All ten individuals weighing 6 to 9 g ( ± SD = 6.7 ± 1.1) 100 m-2 showed evidence of regeneration from fission products. Nine large individuals (>500 g) transferred from Nanwan to Wanlitung and 50 small individuals (<100 g) transferred from Wanlitung to Nanwan in February 1991 showed no evidence of fission during the following year. Fission occurs in small individuals living in shallow tidepools, suggesting that fission probably is triggered by a stressful environment resulting from solar radiation at the unusually low water level of spring tide. Fission of H. atra at Wanlitung results in a population consisting of small individuals.

Population Subdivision of the Tri-Spine Horseshoe Crab, Tachypleus tridentatus, in Taiwan Strait

A field study was conducted at Wanlitung, southern Taiwan, in 1986–1089, to determine the reproductive cycle, development mode, growth rate and population dynamics of the small seastar Patiriella pseudoexigua (Dartnall), which occurs in highly stressful and disturbed intertidal pools in this area. An inverse relationship between gonad index and pyloric-caccum index was only recorded immediately prior to spawning. A short, well-synchronized seasonal spawning occurs in October. When reared at 25 °C, lecithotrophic larvae develop directly, lack a bipinnaria stage, and metamorphose completely on the seventh day after fertilization. The growth curves of field juveniles are linear, those of laboratory-reared juveniles are sigmoid. Juveniles appear in tide pools in spring-early summer of each year. Adults spawn mainly in late fall, enabling spawning to occur in time for the larvae to benefit from the environmentally favorable winter season. Populations in high-tidal pools decrease in later summer, but remain more stable in lowtidal pools and lagoons.