Shirley S. L. Lim

Larval Development of the Dromiid Crab Cryptodromia pileifera Alcock, 1899 (Decapoda: Dromiidae) in the Laboratory

ABSTRACT The complete larval development of Cryptodromia pileifera Alcock, 1899, under laboratory conditions, is described. It consists of only one zoeal and one megalopal stage. This is the first dromiid crab reported to have only one zoeal stage. The zoea is unique in that it lacks the hairlike process on the telson that is characteristic of all other known dromiid larvae. The presence or absence of free-swimming larval stages in the life cycles and their effect on the distribution of the Dromiidae are also briefly discussed.

Maxilliped-Setation Adaptations to Habitat and Sexual Dimorphism of Feeding Claws in Uca perplexa and U. vomeris

Abstract Maxilliped-setation in two Australian fiddler crabs, Uca perplexa (n  =  104) and U. vomeris (n  =  128) was studied and related to the habitats in which these crabs live. Both species were collected from the banks of Myora Springs, North Stradbroke Island, Queensland, Australia. We counted the total number of setae (both plumose and spoon-tipped) on: 1) the inner and outer surfaces of the first and second maxillipeds, and 2) the inner surface of the third maxilliped. In general, there is no distinct sexual dimorphism for both types of setae in the two species. For any given size of crab, significantly more spoon-tipped setae were present in U. perplexa than in U. vomeris, providing further quantitative evidence that fiddler crabs from sandy habitats possess more spoon-tipped setae (an adaptation for processing sandy sediments) than those living in muddy habitats. No significant difference in plumose setation between the two species was generally detected; perhaps plumose setation is of less adaptive significance in terms of habitat adaptation than spoon-tipped setation in these two species. There is generally no sexual dimorphism in the size of the three maxillipeds for both species. Uca perplexa males had longer minor chelipeds than females while U. vomeris males had minor chelipeds that are deeper in the centre than females. These results provide evidence that male fiddler crabs could compensate for their foraging handicap by having longer or deeper minor chelipeds which enable them to scoop larger amounts of substrate.

The Complete Zoeal Development of the Actaeine Crab, Novactaea Bella Guinot, 1976 (Decapoda, Brachyura, Xanthidae) in the Laboratory

The complete zoeal development of the coral reef actaeine crab, Novactaea bella, is reported. Only two zoeal stages are present. The larvae are compared with those from the closely related N. pulchella; the zoeae of the two species differing in the structure of the tips of the antennal protopod, the proportions of the antennal exopod, the tips of the forks of the telson, as well as the setation of the antennal exopod, basal endite of the maxillule, dorsal surfaces of abdominal somites 2 to 5, and lateral margins of the forks of the telson.

Transiting into Inquiry Science Practice: Tales from a Primary School

In this chapter, we describe a case study of the inquiry practices of four science teachers in a primary school in Singapore. We were motivated to carry out this study to address two issues. Firstly, while there has been a significant amount of research into the nature of inquiry science, more recent discussions have pointed to the smaller amount of research on teachers’ instructional practices of inquiry in the classrooms. For teachers transiting into inquiry practice, concrete descriptions and analyses of what inquiry looks like in practice, when and how it occurs can be helpful. Secondly, teachers were concerned that inquiry science, as described in literature, was impossible to implement in countries such as Singapore where there are usually large class sizes and a strong focus on preparing students for national examinations. Our study surfaced nuances in the teachers’ inquiry practice that sought not only to address local issues but also reflected their tacit experience and beliefs. Importantly, this study also examined the tensions teachers faced and the factors that contributed to their dilemma and decisions as they adapted their teaching practices to their beliefs and interpretations of what constitute inquiry science. This line of inquiry would contribute towards efforts in supporting teachers who are transiting into inquiry science practices.

To flee or not to flee: characterising differentiated anti-predatory responses of two mangrove crabs

In a previous study, lethal effects of mudskipper (predator) presence were detected in the mangrove brachyuran Paracleistostoma depressum but not Haberma nanum. In addition, these effects were sex specific (male: non-significant; female: significant), suggesting differences in anti-predator behaviour. To validate this, predator avoidance strategies of the two prey species were investigated for the variables ‘species’ and ‘sex’. Ex situ responses of 40 crabs (10 per sex per species) to a mudskipper model were video-recorded. Three stimuli were given in the sequence of (A) upper torso appearance, (B) full body appearance and (C) lunge towards crab. Innate behaviour to any innocuous signal was ruled out by replacing the mudskipper model with a rectangular block. Lastly, predator recognition capabilities in terms of shape and presence of eyes were tested using five models with increasing similarity to the predator model. P. depressum and H. nanum share the same suite of observable anti-predatory behaviours: “freeze”, “sit” or “run”. However, varied strategies were observed. Instead of flight, P. depressum “sit”, and reacted most notably in the last stimulus. In contrast, H. nanum reacted early in the onset of impending threat with “run”, with diminished responses despite the increase in signal strength. Contrary to prediction, the factor ‘sex’ was not statistically significant in either species. Predator recognition capabilities were ascertained in both prey species, as behaviours were different after the predator model was replaced. H. nanum displayed greater sensitivity for threat perception by withholding the flight behaviour when uncertain. This keen sense for threat recognition coupled with its flight strategy may be key to explaining the exclusion of H. nanum from the predator’s diet.

Constraints imposed by the major cheliped on burrow construction in the male fiddler crab, Uca annulipes (H. Milne Edwards, 1837)

The burrows excavated by male Uca annulipes at a lagoonal shore on Pulau Hantu Besar, an offshore island of Singapore, are generally less acutely bent, i.e., have significantly smaller mid-angles, than the burrows of females. In an ex situ study, burrows dug by males with the major cheliped removed, and by males with intact major cheliped, were cast with wax. Seven non-angular burrow morphological parameters (burrow diameter, total burrow depth, burrow neck height, curved burrow length, horizontal length, chamber diameter and burrow volume) and two angular variables (mid-angle and ground-angle) were compared to determine if sexual dimorphism in burrow curvature was due to the effect of the major cheliped on burrow excavation. A similar experiment using females with two intact chelipeds and one cheliped removed was conducted to determine if male crabs without the major cheliped dug burrows with dimensions similar to those of females with one cheliped removed. Mean mid-angle of burrows (± SE) was 24.9 ± 1.3° and 16.0 ± 1.0° for males whose major chelipeds were removed and with major intact chelipeds, respectively. Of all the burrow morphological parameters, only the mean mid-angle differed significantly between the two groups of crabs. Female crabs (with and without cheliped removal) did not excavate significantly different-shaped burrows (mid-angles: 20.7 ± 2.1° and 18.2 ± 1.5°, respectively) suggesting that removal of cheliped did not affect burrow architecture. The curvature of the burrows of males that had the major cheliped removed was not significantly different from those of females with one cheliped removed (mid-angles: 24.9 ± 1.3° and 20.7 ± 2.1°, respectively). Results of the study showed that the major cheliped in a male U. annulipes is most likely to be responsible for the sexual dimorphism in curvature of the burrows.