FROGS vs LEECHES
Indira Gandhi National Forest Academy
Preliminary observation of frogs in Periyar Tiger reserve, Kerala, showed few individuals infested by leeches. This led to a study to probe the kind of interaction between leeches and frogs, preference, kind of association, effect of environment characters. The hypothesis was that the leeches were parasitizing these frogs as alternative hosts and fed on them during opportunistic encounters, or alternatively used frogs as a mode of transportation in the forest floor.
The study was based on visual encounter surveys conducted in various segments of the reserve. Snout –vent length (SVL), site of encounter, presence of leech on body, status of feeding were recorded during day and night sampling. A total of 190 frogs, representing 8 species, were collected during the study period of which 39 were positive for leech presence.A controlled experiment was carried out to determine ‘preference’ of leeches, if any, for certain species of frogs.
The hypothesis that bigger frogs harbor more leeches stood invalid. Such leech presence on frogs was maximum in the wet evergreen habitat: on leaf litter and undergrowth, close to water source and did not vary with time of sampling. This could be due to coinciding leech habitat. When all other environmental parameters were controlled for in the experiment, maximum number of leeches was found on Clinotarsus sp and only one third of mounted leeches were found to be feeding.
This study has reported the interaction of leech and frogs. Whether it is parasitism or not is to be probed further in addition to how leeches can sense presence of frogs. The effect of such infestation might significantly affect population dynamics of frogs. A toad population is known to have gone locally extinct due to predation pressure by leeches. The indirect effects range from disease transmission, reduction of immunity and improper development of egg clutches.