Behaviour
Studies associated with the behaviour of T. bayeri is rare. One of the reason is because the organism is small and very hard to work with. However, during the field observation in Heron Island, periodic nodding of the head were observed repeatedly throughout the period. This behaviour is also evidences in other researcher projects (Marshall 1999; Jensen 1992). Nodding behaviour can be refers to the raising and lowering of the anterior section of its foot off the substrate. However, the reason of this behaviour is still unknown. Studies done previously also found no association of the species with any algal type (Marshall, 1999; Handeler & Wagele 2007; Wagele et al. 2010).
During Heron Island trips, an experiment has been done to account for T. bayeri behaviour. The aim of the experiment is to investigate if the species is more active during the day or it is nocturnal.
Hypothesis: T. bayeri is more active during the day and move slower during the night.
Method:
Sampling were done at Shark Bay, east of the research station, during low tide from the 20th to 22nd of September 2011. Size of T. bayeri collected were ≥10 mm in length, where the smaller one were left in the wild. The sample were collected in a container with sand substrate, broken coral, and algae pieces. The specimens were keep in the aerated tank. A total of 16 samples were collected, however, only seven were available for the study. The experiment is design by measuring the time taken individual will take to travel 7.75 cm distance to calculate the speed. The experiment is conducted in 15.5 cm x 15.5 cm tray during day (9am) and night (8:30 pm). Temperature were recorded every each test. Seven T. bayeri were used in the studies with a size range from 11 mm to 19 mm. Three replicate for each individual were conducted per each time of the day. Hence a total of 21 replicates were conducted for each time of the day. Day time experiment were conducted under normal laboratory condition. Night time experiment were done in dark room. The observation were done via red light by the use of torch light that filter through 787 lee filters. The tray is fill with 0.5 cm of sand and 1 cm of water above the sand. The movement is track by placing transparent board over the tray and draw according to the movement starting from the tips of the rhinophores. Stopwatch started when the slug started to make its first movement and stopped once the slug reach the edge of the tray. However, if the slug started to stay in one place more than 30 seconds, the timer stopped (only apply to night experiment). Pictures of the tracking is taken and analysed using ImageJ program.
The results support the hypothesis stated that T.bayeri would be more active during the day and move slower during the night (p<0.05). This might be because they are not nocturnal. Many literatures address that most Elysiidae can obtain chloroplast from their algae food and use them to produce their on energy via photosynthesis (Cimino 1998; Gosliner 1995). Photosynthesis need sunlight, therefore, it is possible that the reason they are more active during the day is because of the necessity of sunlight in photosynthesis. However, studies associated with phosynthesis evolution of Elysiidae have only been done in T. hopei not T. bayeri (Gavgnin et al. 1993). However, there are strong parallel evolution evidences which suggest that photosynthesis using chloroplast from the algae food is common in Elysiidae (Cimino 1998; Gavgnin et al. 1993). More studies should be done on T. bayeri to account for photosynthesis pigments to ensure that one of the reason they are more active is because of necessity of light for photosynthesis reaction. One experiment could be done is to test them at different time of the day, where different sunlight is exposed. The experiment will ensure the use to sunlight by the organism. Nodding behaviour also seen more during the night, therefore, studies can be done to focus on their behaviour for better understanding of the organism.
Another possible reason may be because during of predations. As Thuridilla have striking colour they might have to search for a place where they can hide during the day. However, with their dark colour, they might not need to move to search for a place to hide as they are more blend in the environment.
The experiment could be improve by familiarized the organism in the conditions before the timer start. The condition of the wild should match the environment in the tray e.g. temperature. More experiment should be done for T.bayeri from different place of the world e.g. Guam, Thailand, Philippines, or Indonesia. The experiment could be expand by testing the same experiment on other colour forms (T. ratna and T.gracilis) from different part of the world. In addition, it is possible to observe their behaviour under other circumstances such as temperature, time of the day, water level (stimulate tide), or seasonal effect.
Comparison experiment:
The experiment was done by Low Hong Wen Dolyce based on Plackobranchus ocellatus. The species belong to the same family (Cimino 1998). They also feed on the cytoplasmic contents of the algae. However, the photosynthetic lamellae have been discovered in this species. Therefore, the species have strong correlation with chloroplast in the algae Hirose 2005.
Figure 2: Bar graph showing crawling speed of P. ocellatus. Grey bar showing crawling speed during morning experiment. The graph does not show crawling speed at night as the average speed is 0 cm/s (Left). Pictures of P. ocellatus taken by Low Hong Wen Dolyce (right).
Figure 2 indicate that P.ocellatus is also more active during the day. Due to the presence of Photosynthetic lamellae, it is possible to interpret that they need sunlight for photosynthesis that is why they are more active at during the day to move to the area where maximum sunlight can be obtain. However, this might be different from T. bayeri, therefore, it is wise to find out whether they have photosynthetic related structure or not.
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