ACBTE Vol. 3:81-83, 1993
A method for comparative morphogenesis of teeth in mammals:
An easy way to catch soricine shrews alive.
Kazuhiro KOYASU, Hajime HANAMURA and Takeo MIYAO
The Second Department of Anatomy,
School of Dentistry, Aichi Gakuin University
Nagoya 464, JAPAN
INTRODUCTION
For the study of comparative morphogenesis of teeth, which includes
enamelogenesis, one should first prepare materials. Even in the limited
taxon of living mammals (Class Mammalia), there exist 21 orders, which contain
4327 species (Corbet and Hill, 1991). Most of these species belong to Eutheria
(placental mammals) which divided from Metatheria (marsupial mammals) over
100 million years ago during early Cretaceous (Kielan-Jaworowska et al.,
1979).
Within all eutherian mammals, insectivores (shrews and moles: Order
Insectivora) are the most primitive mammals. Because all recent placentals
are thought to be derived from this stock in Mesozoic, it seems especially
important to consider this group as the materials for comparative study.
It seems rather difficult to get both fetus and neonates of soricine
shrews in the field compared with bats that breed in colonies (e.g. Koyasu
and Mukohyama, 1992). It will contribute to comparative study of tooth
germs of insectivores if the soricine shrews (Subfamily Soricinae) can be
developed as new laboratory animals. It seems very important to catch them
alive in the field for this purpose, so we will explain how to catch shrews
alive and identify them.
INSTRUMENTS AND METHOD FOR CATCHING SHREWS
Recently, Abe (1992) explained general methods for catching insectivores.
Shrews (family Soricidae) are divided into three groups in taxonomy. Of
these, soricine shrews are distinctive with red-pigmented teeth. Others,
crocidurine and scutisoricine shrews, generally have non-pigmented ones
(thus they are called "white-toothed shrews"). Some genera in
Tribe Neomyini of soricine shrews, however, have non-pigmented teeth (e.g.
Anourosorex and Chimarrogale, Plate 1).
Soricine shrews are ecologically divided into two groups, red-toothed
shrews and water shrews. The life of the former depends on humid litter
(see Plate 2 for their habitat), and the latter have a semi-aquatic life
(Abe, 1992). White-toothed shrews live on comparatively dry land. Churchfield(1990)
thought the difference in litter size between soricine and crocidurine shrews
reflected their differences in gestation periods and development of the
young at birth. The way to catch shrews is different in each of these three
kinds of life styles.
White-toothed shrews contain both Suncus and Crocidura. Suncus is
well known as a laboratory shrew (Oda et al.,1985). This shrew is easily
captured by using mesh-cage traps and Sharman's traps. Tooth germ development
in Suncus have already been described (Hanamura et al.,1983; Kondo, 1985).
Crocidura is rather difficult to catch, but the recent success at domesticating
it (Ohno et al.,1992) will make it possible to use it for laboratory works.
Red-toothed shrews, which contain many species of the genus Sorex,
are easily captured by pitfall traps. For their successful introduction
to the laboratory, however, frequent collections (every two hours at least)
of living animals at night are needed. Bigger pitfall traps are recommended
that can contain nest materials and food, but more effort will be needed
digging holes in the ground. A special kind of instrument (Plate 3) for
this purpose makes it easier to dig a big hole in a short time. Any kind
of cups, cans or half-cut bottles can be used as pit-fall traps by setting
them in the above holes.
Water shrews, Chimarrogale himalayica, whose life depends mainly on
a semi-aquatic habitat, can be caught alive by using mesh-cage traps with
living fish as bait. Because of their distinct life style, much effort
will be needed to care for them before their successful breeding under capture.
IDENTIFICATION OF SHREWS IN THE FIELD
The knowledge of the biogeography of shrews is very important for
the identification of shrews. In Japan, red-tooted shrews occur in Hokkaido,
Honshu, Shikoku and their adjacent islands. Except Hokkaido and nearby
islands, this kind of shrew lives mainly in alpine and sub-alpine zones.
White-tooted shrews, on the contrary, are very rare in Hokkaido, and common
in the lower land in Honshu, Shikoku, Kyushu and their adjacent islands.
Suncus live inside and/or outside the house on the Ryukyu Islands and some
islands of Kyushu. Chimarrogale occur in the mountain streams of Honshu,
Shikoku and Kyushu.
In dead specimens, if the head skin is removed, their remarkable shape
and size are distinctive as shown in Plate 4. In Hokkaido, there live four
species of red-tooted shrews. One (S. minutissimus) is very rare but if
seen, its considerably smaller size (body weight is about 2g.; the smallest
mammal in the world) will make it easy to distinguish from other species.
Three other species, S. unguiculatus, S. caecutiens and
S. gracillimus are generally distinguished by the difference of their body
size.
S. gracillimus is considerably smaller than other two species, but larger
than S. minutissimus. Usually S. unguiculatus are larger than S. caecutiens.
Sometimes, especially in summer, it is difficult to distinguish these two
species because the young of S. unguiculatus are the same size as adult
S. caecutiens. In this case, the differences in the size and shape of the
front feet are the most convenient characteristics to distinguish them (Fig.1).
"Long-clawed shrew", the common name of
S. unguiculatus was named after this remarkable feature.
Acknowledgement
The authors thank Dr.M.Harada of the Laboratory of Experimental Animals,
Osaka City University Medical School for providing us an opportunity to
access the specimen of Sorex hosonoi under his care.
References
1. Abe,H.: Mammal.Sci.,31:139-143,1992.
2. Churchfield,S.: The natural history of shrews. Christopher Helm, pp.178,1990.
3. Corbet,G.B. and Hill,J.E.: A world list of Mammalian Species, 3rd ed.
Oxford Univ. Press, pp.243, 1991.
4. Hanamura,H.,Shigehara,N. and Oda,S.:J. Growth, 22:28-43,1983.
5. Kielan-Jaworowska,Z.,Bown,T.H.and Lillegraven, J.A.:Mesozoic Mammals
(Lillegraven, J.A.,Kielan-Jaworowska,Z.and Clemens,W.A eds). Univ. California
Press,221-258, 1979.
6. Kondo,S.: Aichi-Gakuin J.Dent.Sci.,23:697 -730, 1985.
7. Koyasu,K and Mukohyama,M: Structure, function and evolution of teeth
(Smith,P. and Tchernov,E. eds). Freund Publ.House,115-123, 1992.
8. Oda,S.,Kitoh,J.,Ota,K.and Isomura,G.: Suncus murinus: biology
of the laboratory shrew. Jpn. Sci. Soc.Press, pp.535,1985.
9. Ohno,K.,Niwa,Y.,Kato,S.,Koyasu,K.,Oda,S. and Kondo,K.:Exp. Anim., 41:449-454,1992.
Plates
Plate 1. Photograph of Anourosorex squamipes from Taiwan.
Plate 2. Landscape of habitat of Sorex hosonoi that is sympatric with S.
shinto at the type locality.
Plate 3. Instrument to dig holes for pitfall traps.
Plate 4. Difference of shape and size of red-toothed shrews in Honshu.
From left to right, Sorex hosonoi, S. shinto and S. sadonis.