Maro, Shabanov (2005) Mechanisms of dispersal of the common toad and the features of its populations in recently colonized habitats

{"translated":"Maro A. N., Shabanov D. A. Mechanisms of dispersal of the common toad (Bufo bufo (L. 1758); Amphibia, Anura) and features of its populations in recently colonized habitats // Materials of the First Conference of the Ukrainian Herpetological Society. – K.: Zoological Museum of the NNP of the NAS of Ukraine, 2005. – pp. 107–110.\nMechanisms of dispersal of the common toad (Bufo bufo (L., 1758); Amphibia, Anura) and features of its populations in recently colonized habitats\nA. N. Maro, D. A. Shabanov\nKharkiv National University named after V. N. Karazin, Svobodi Square, 4, Kharkiv 61077\nThis work is devoted to the studies of common toad Bufo bufo (Linnaeus, 1758) artificial moving to new habitats consequences that was performed in Kharkov region in 1994. The natural dispersion of toads has been found to occur in two ways. The first way includes a transfer of tadpoles with water. The second way includes incoming of toads into the reservoirs located between a former place of spawning and a ground habitat of toads settled by toads upon their metamorphosis. The new‑founded groups of breeding (local populations) differ from their progenitor groups with the substantially smaller size of males and bigger size of females. It seems that on settling of new habitats, common toad males tend to accelerate their maturing, while females tend to accelerate their growth.\nFor toads of the genus Bufo it is characteristic to form well‑isolated breeding groups (local populations) associated with spawning water bodies and maintained by philopatry. Each breeding group possesses uniqueness determined by its history, the features of inhabited habitats and interaction with neighboring groups. Studying the formation of new breeding groups during toad dispersal can be very useful for understanding their specifics. In 1994 in the Kharkiv region, with the participation of one of the authors of this work, artificial dispersal of common toads (Bufo bufo (Linnaeus, 1758)) was carried out. In the course of studying its consequences we examined samples of common toads from eight habitats listed below (a total of 244 sexually mature individuals caught during spawning, of which 84 females and 160 males) and conducted field observations of their spawning.\n1. Starytsia: bank of the Seversky Donets River in the vicinity of the biological station of KhNU named after V. N. Karazin in the village of Haidary Zmievskyi district; a shallow old river channel in a moist oak forest with blackthorn thickets; 9 females, 9 males.\n2. Koryakov Yar: vicinity of the biological station of KhNU; silty pond in oak forest; 22 females, 27 males.\n3. Iskiv Pond: vicinity of the biological station of KhNU; beam pond between oak forest and meadow; 4 females, 13 males.\n4. Lower Pond, Pyatykhatky: vicinity of the village Lesne of the Kharkiv River basin; lower of three ponds in the Ocheshetyansky ravine in oak forest; 15 females, 19 males.\n5. Upper Pond, Pyatykhatky: same location, upper of three ponds; 8 females, 16 males.\n6. Upper Pond, Olkhovaya Ravine: vicinity of the village Ruska Lozova of the Kharkiv River basin, upper of seven ponds in a wide ravine passing through upland oak forest; 9 females, 26 males.\n7. Lower Pond, Olkhovaya Ravine: 6th pond at the ravine outlet in the floodplain of the Kharkiv River; 7 females, 22 males.\n8. Dobra Ravine; pond in the ravine flowing into the floodplain near Olkhovaya Ravine; 10 females, 28 males.\nEcologically habitats 2–8 are very similar and typical for the common toad in the Kharkiv region; habitat 1 differs markedly from them. Geographically the studied points form three groups, the distance within which does not exceed 5 km: 1–3; 4 and 5; 6–8. Breeding groups at points 1–3 are old, and 4–8 are young; the youngest local populations are at points 5 and 8. Genealogical links of the studied populations: 3→4→5; 3→6→7→8. Dispersals 3→4 and 3→6 were performed artificially in 1994 by moving non‑spawning toads caught during spawning in Iskiv Pond. About 200 individuals of both sexes were transferred to Pyatykhatky, about 100 to Olkhovaya Ravine; only a small part of the thriving breeding group of Iskiv Pond was removed. For colonisation, water bodies ecologically similar to Iskiv Pond but located in a well‑studied forest massif surveyed by Kharkiv herpetologists, where common toads were absent, were chosen. Subsequent spread of toads proceeded naturally, with 4→5 occurring against the water flow in the pond system, 6→7 with the water flow, and 7→8 across a watershed. In 1995 and 1996 during the spawning of common toads they could not be found in the lower pond in Pyatykhatky. Apparently, the introduced toads spawned in the new water body but did not return to it subsequently. Development of the breeding group was linked to the return of offspring of the founder individuals to the pond where they developed.\nIn Olkhovaya Ravine, where toads were transferred to the upper pond, they quickly spread throughout the system connected by a common watercourse. Obviously, their dispersal was associated with the transport of tadpoles by water. In Pyatykhatky the middle pond (situated between the lower and upper) was colonised considerably later than the lower one, and the upper pond (habitat 5) was colonised last. In 2004 only a few sexually mature toads arrived at the upper pond in Pyatykhatky for spawning, and in 2005 their number increased by more than an order of magnitude. Clearly, a different dispersal mechanism, directed against the water flow, was used in this case. Observations made in 2005 on the middle pond are crucial for understanding it.\nWe observed that most pairs of toads in amplexus on the middle pond moved towards the lower pond. Females approached the pond carrying males, or met them in the water. Then the pairs moved towards the dam retaining the pond, exited onto the bank and slid into the lower pond. Only some pairs remained in the middle pond and did not move further. Probably, during the dispersal of metamorphs from the lower pond some of them migrated to the middle pond. Upon reaching sexual maturity, moving towards their development site, they descended into the ravine and entered the middle pond on their way. Most toads passed it and reached the final point of their route, but some did not reach it and spawned in the middle pond. Their offspring returned to the middle pond and over time colonised the upper one.\nThus, it can be hypothesised that the colonisation of new spawning sites by toads occurs in two ways: by transport of tadpoles with the water current and by entering water bodies situated between the previously occupied spawning site and the terrestrial habitat of the dispersing individuals.\nThe comparison of samples was carried out on 24 morphometric, 21 qualitative and 8 discrete traits of toads, as well as on 29 ratios (relationships of morphometric traits). Principal component analysis was performed on normalised mean values in the samples using the Statistica for Windows package (Fig. 1). It is evident that females were less variable than males, and the mutual arrangement of their samples on the principal component plane corresponded better to the genealogical relationships among breeding groups. Differences between samples from the vicinity of the KhNU biological station (1–3) exceed differences between samples from young breeding groups, which in most cases are closest to the sample from the parental habitat (3). Males from the youngest breeding groups (5 and 8) differ most strongly from the others in their absolute sizes, and are very close to representatives of the parental breeding group in qualitative, discrete traits and body proportions.\n[IMG_1]\nYoung breeding groups differ highly reliably in the body sizes of their constituent individuals (Fig. 2). In the colonised habitats during spawning (and forming pairs) very small males (body size 45–60 mm) participate. These are probably young individuals not taking part in the spawning of stable populations. The second peak of male occurrence in the “young” breeding groups (65–70 mm) corresponds to their characteristic size in long‑settled habitats. Paradoxically, the participation of “undersized” males in spawning is combined with larger female sizes. Since in the colonising upper pond in Pyatykhatky (sample 5) both small males and large females arrived for spawning simultaneously, they are similar in age. Probably, these females exhibited especially rapid growth. Thus, it can be concluded that in the colonisation of new habitats male common toads accelerate maturation, while females accelerate growth. The discovered phenomenon requires further study (in particular, determination of age and growth rate of toads).\nThe authors express gratitude to A. V. Korshunov, M. A. Kravchenko and T. S. Fomenko for assistance in material collection and field observations."}