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1. 2 meadows Road 820 1998 8 47 2 16 7 1 7 0 7 8 4 1 8 ditches 1 The values only concerned 4 samples As the 4 others placed in the same box the figure was not taken into account for the calculation of this mean value 4 Discussion Even though snail investigations were performed on 11 populations of G truncatula living in siliceous ha bitats and subjected to the same period of summer drought in 1996 1997 and 1998 the results obtained could be due not only to the altitude of sites studied but also to other factors such as microclimate Under these conditions these findings might not for the mo ment be generalized to snail populations living in other countries as snail aestivation is dependent on local cli matic variations which occur in the habitats of G trun catula The percentage of G truncatula able to survive drought in the highland populations might by explai ned by two perhaps complementary hypotheses As the local climatic conditions from the highland sites were different from those existing in the Haute Vienne de partment with a higher annual rainfall and more rela tive humidity the first assumption would be to admit a slower drying of these snail habitats in June July than in lowland sites permitting snails to burrow into the soil or to hide better in the deepest places of the habi tat The second hypothesis would be to consider the greater ability of these highland G truncatula to bur row th2. mm 2 These snails were alive after the flooding of dried soil with water 3 Partial burrowing 3 snails with shell buried by 50 14 snails with shell buried by 75 se last authors 30 of adult snails were completely buried in the soil on day 4 following the beginning of experiment while an incomplete burrowing was no ted for 20 of other snails with the apex of the shell still visible The results reported in this note demons trated that burrowing was more developed in the high land populations of G truncatula than in the lowland snails To explain this finding the most valid hypo thesis would be to consider snail burrowing as a phy siologic response of these highland G truncatula to summer drying The percentages of buried snails in the third investigation 13 0 15 0 of juvenile snails and 5 8 8 3 of adults could be related in our opi nion to experimental conditions used in the laborato ry and would probably be higher in the field An argu ment to support this last hypothesis was the number of live snails which exited from soil samples after their collection in dried sites and flooding with water Table 2 References Bednarz S 1960 On the biology and ecology of Galba truncatu la M ll and cercariae of Fasciola hepatica L in basin of the river Barycz Acta Parasitol Pol 8 279 288 De Massias E 1995 Contribution l tude des g n rations an nuelles chez Lymnaea truncatula M lle
3. of snails surviving after aestivation is higher in the highland than in the lowland areas it was less than 20 in the habitats of G truncatula below 300 m in altitude Ron delaud amp Morel Vareille 1975 and increased up to 55 in those located at 800 1 200 m de Massias 1995 Several authors such as Mehl 1932 Peters 1938 Roberts 1950 Bednarz 1960 Rondelaud amp Morel Vareille 1975 or Smith 1981 for example have al ready reported that the newborns and the juvenile G truncatula from the lowland populations were more re sistant to summer drought than older snails However as the conditions of aestivation in these populations depended on seasonal climatic variations which occur red in snail habitats several differences could be no ted In central England for example many snails sur vived with the aperture attached to the mud surface Kendall 1949 whereas in several sites of central France alt lt 300 m the alive snails were few in num ber and numerous empty shells were found on the sur face of the soil or in the upper zone of soil cracks Ron delaud amp Morel Vareille 1975 By contrast little in formation is available on the aestivation of G trunca tula in the highland habitats In the Massif Central alt 820 m a few empty shells on the soil surface we re found after a 4 week summer drying of the habitat and there was only a decrease by 50 in the number of surviving s
4. populations of Gal ba truncatula Tableau 1 Taux de survie et hauteur des coquilles des mollusques ayant surv cu l estivation dans des populations de plaine et d altitude de Galba truncatula qq Station Altitude Year Area Total number of live snails Shell height of in m studied surviving snails in m2 Count Count Count n 3 in mm n n 2 and survival rate in Open drainage 206 1996 4 97 27 31 31 9 1 8 0 5 furrows in 227 2 51 11 13 25 4 1 9 0 7 meadows 254 2 42 15 17 35 7 2 0 0 6 282 2 48 9 11 22 9 1 8 0 6 Road 260 1997 10 285 152 90 31 5 1 9 0 6 ditches 1998 10 252 191 74 29 3 1 8 0 7 280 1997 10 211 115 62 29 3 2 1 0 8 1998 10 245 167 81 33 0 1940 7 Open drainage 806 1996 4 106 11 67 63 2 3 2 0 9 furrows in 848 47 5 37 78 7 2 9 0 8 meadows 871 2 53 5 31 58 4 2 9 0 7 Road 820 1997 10 225 25 174 77 3 3 1 1 1 ditches 1998 10 255 32 206 80 7 2 8 1 0 900 1997 10 322 66 224 69 5 3 2 1 0 281 75 202 71 8 3 0 0 9 1998 10 1 Count n 1 performed at mid June when each area was still covered with a 5 cm layer of water Count n 2 made at the onset of July when the soil started to crack Count n 3 made two days after the flooding of each area with water 2 Survival rate count n 3 count n 1 3 Mean values SD Table 3 gives the percentage of snails buried in the soil during an experimental drying of their breeding boxes
5. under laboratory conditions 20 C The percen tages of snail buried in the soil were higher in the highland population 13 0 and 15 0 of juvenile snails for xample instead of 4 0 and 7 7 in low land snails In the lowland population only young snails buried whereas 5 8 and 8 3 of adults in the highland population were also burrowing Despite a meticulous examination of the soil surface with a ste reomicroscope juvenile snails could not be seen be cause they were completely buried In contrast partial burrowing of adult snails was observed with a shell buried by 50 3 snails or 75 14 snails 5 ALTITUDE AND AESTIVATION OF GALBA TRUNCATULA 215 Table 2 Numbers of live Galba truncatula shell heights and durations of snail re activation after the flooding of dried soil samples with water Tableau 2 Nombre de Galba truncatula en vie hauteur des coquilles et dur e de leur reprise d activit apr s l immersion d chantillons de sol dess ch dans l eau Station Altitude Year Number Mean values SD in m of samples Number of live Shell height Duration of snail snails per sample mm re activation in water hours Open drainage 227 1997 6 15 3 7 2 1 6 0 5 7 6 2 1 furrows in 282 12 5 9 7 1 7 0 4 8 0 1 9 meadows Road 280 1998 10 20 5 10 4 1 6 0 4 8 9 2 6 ditches Open drainage 806 1997 6 36 3 14 1 2 1 0 9 8 2 1 8 furrows in 871 41 3 10 5 1 9 1 0 8 5 2
6. Ann Limnol 37 3 2001 211 217 Influence of aestivation on the survival of Galba truncatula Mollusca Gasteropoda populations according to altitude M D Goumghar 2 D Rondelaud G Dreyfuss M Benlemlih Keywords Galba truncatula aestivation altitude Massif Central Field and laboratory studies on 11 populations of Galba truncatula were performed to determine the survival rate of snails after aestivation to specify the range of their shell heights and to establish the percentage of G truncatula which burrowed in soil when summer drying occurred These investigations were performed using six lowland populations living in central France alt 206 282 m and five highland populations located in the Massif central alt 806 900 m The survival rate of G truncatu la after flooding dried soil with water was significantly higher in the highland than in the lowland populations 69 5 80 7 in road ditches for example instead of 29 3 33 0 The mean shell heights of surviving snails and the durations of snail re acti vation in water did not show any significant variation whatever the origin of snail population The percentages of snails buried in drying soil were higher in the highland population 13 0 and 15 0 of juvenile snails for example instead of 4 0 and 7 7 in lowland snails In the lowland population only young snails buried whereas 5 8 8 3 of adults in the highland popu lation were partially burrowing The lo
7. antly higher P lt 0 01 in each case in the highland populations than in the lowland ones Several differences P lt 0 05 could be noted between the rates of the high land populations or those of the lowland ones when snails were living in open drainage furrows In contrast in road ditches there were no significant differences between the rates of the highland populations those of the lowland ones or between 1997 and 1998 for each site studied The shell heights of surviving snails were slightly higher in the case of highland populations Ho wever the mean values did not show any significant variation whatever the mode of comparison Table 2 gives the number of surviving snails their shell height and the duration of snail re activation when samples of dried soil are placed in spring water After activation in water surviving snails were signifi cantly more numerous F 26 4 77 P lt 0 01 in the highland populations of G truncatula than in the others The standard deviations of shell heights were greater in the former populations than in the latter ones but there were no significant differences between the mean values The mean duration of snail re activation in water ranged from 7 6 to 8 9 hours and did not show any significant variation 214 M D GOUMGHAR M RONDELAUD G DREYGUSS M BENLEMLIH 4 Table 1 Survival rates and shell heights of surviving snails after aestivation in the lowland and highland
8. area of these snail habitats was less than 5 m in swampy meadows Vareille Morel et al 1999 the ex periment was replicated in 1997 and 1998 in four road ditches each colonized by an abundant population of 3 ALTITUDE AND AESTIVATION OF GALBA TRUNCATULA 213 snails Every year one two or five 2 m2 areas were chosen in each site for their high numbers of snails more than 40 snails per area Table 1 Each area se lected was individually isolated from the rest of the ditch by the construction of two 25 cm high dykes with packed mud and stones A first count of live snails was performed at mid June when each area was still covered with a 5 cm layer of water The live snails and empty shells present on mud were again counted and removed from every area when the soil started to crack at the onset of July When the first crack in the soil was 1 cm wide six hundred litres of spring water were gradually poured in each area for six hours to flood dried substratum and to re activate aestivating snails A third count of surviving snails was performed two days after the flooding of each area and their shell heights were measured using a calliper rule The second investigation was performed in 1997 and 1998 under laboratory conditions to verify the results of the first experiment Six eight or ten samples of soil surface of each sample 1 dm2 soil thickness 3 4 cm weight 100 150 g were collected in three lowland and three highlan
9. cal climate of the sites studied in the Massif central and the ability of snails to burrow into the mud when stagnant water disappeared in July might explain the higher survival rate during aestivation Influence de l estivation sur la survie de populations de Galba truncatula M ller Mollusca Gasteropoda en fonction de l altitude Mots cl s Galba truncatula altitude estivation Massif Central Des tudes sur le terrain et au laboratoire sur 11 populations de Galba truncatula vivant en plaine ou en altitude ont t r a lis es pour d terminer le taux de survie des mollusques apr s l estivation pr ciser la gamme de leurs hauteurs de coquilles et tablir le pourcentage de G truncatula qui s enterrent dans le sol lors de l ass chement estival Ces observations ont t effec tu es en utilisant six populations de plaine vivant dans le centre de la France alt 206 282 m et cinq colonies d altitude situ es dans le Massif central alt 806 900 m La survie des limn es apr s l inondation du sol dess ch est significativement plus le v e dans les populations d altitude que dans celles de plaine 69 5 80 7 dans les foss s de route par exemple au lieu de 29 3 33 La hauteur moyenne des coquilles des mollusques survivants et la dur e de leur reprise d activit dans l eau ne pr sentent pas de variation significative quelle que soit l origine des mollusques Les pourcentages de limn es en
10. comprises metamorphic rocks The low land stations have underlying two mica granites or migmatites whereas the substratum of highland sites is constituted with augen gneiss Water is running in the ditches from the beginning of October to mid July and summer drying of habitats occurs from the end of July to the end of August so that its length is similar in the four stations 6 weeks in 1996 5 in 1997 and 6 in 1998 Water is oligocalcic with a pH ranging from 6 5 to 6 7 an electric conductivity from 55 0 to 70 5 uS cm a calcium ion content from 9 7 to 15 5 mg l and a nitrate content from 0 1 to 1 1 mg l Goumghar 2000 In the 11 sites the maximum shell height of adult snails scarcely reaches 8 mm The climate is continental but it is more under ocea nic influence in the department of Haute Vienne than in the Massif central Average annual rainfall was 850 mm in the lowland stations and 1039 mm in the highland sites However in the four stations the monthly rainfall during the investigations in the field was close in the four sites 28 33 and 31 mm in the lowland sites in July 1996 July 1997 and July 1998 respectively and 32 35 and 35 mm in the correspon ding highland sites for the same periods Goumghar 2000 2 2 Protocol of experiments The first investigation was performed in 1996 in se ven habitats of G truncatula located at the peripheral _ extremities of open drainage furrows However as the mean
11. d habitats when the soil cracks were 0 7 1 3 cm wide Table 2 Each sample of dried soil was then placed in a 10 cm deep layer of spring water All trials were performed in a room sub jected to temperatures diurnally fluctuating from 6 C to 22 C Soil samples were kept under constant sur veillance to determine the duration of each snail re ac tivation after placing in water to count live snails and to measure their shell height with a calliper rule The third investigation was performed in 1998 under laboratory conditions and repeated in 1999 to determi _ ne the percentage of G truncatula that burrowed in soil during an experimental drying A lowland and a highland population of snails were used in this experi ment Every year a total of 200 juvenile snails 1 2 mm in height and 120 adults 4 6 mm were col lected at mid June from each population Breeding boxes of 0 66 m2 each were constituted with a 5 cm layer of soil covered with a 2 cm layer of water origi nating from each aforementioned site One hundred young snails or 60 adults were then placed in each breeding box and the contents were allowed to dry by natural evaporation in a room subjected to diurnally fluctuating temperatures from 6 C to 22 C An hour ly surveillance was performed to determine the num ber of snails that buried in the drying soil and the conditions of this process snail completely buried or partial burrowing by 50 or 75 Six litres of wa
12. e soil The low numbers of live snails removed from these highland sites after the second count Table 1 indicated that numerous snails have buried into the soil before the total disappearance of stagnant water and suggested that the stimulus triggering snail burro wing might be changes happening in hydrochemistry when summer drought proceeded Snail burrowing in soil before aestivation was alrea dy noted by Bednarz 1960 in the field or by Moukrim amp Rondelaud 1992 during an experimental drying of snails under arid climate conditions According to the 216 M D GOUMGHAR M RONDELAUD G DREYGUSS M BENLEMLIH 6 Table 3 Numbers Galba truncatula buried in the soil during an experimental drying of snail environment under labo ratory conditions Tableau 3 Nombre de Galba truncatula enfouies dans le sol lors d un ass chement exp rimental de leur milieu de vie dans les conditions du laboratoire i Number of alive Galba truncatula Type of habitat Stage of 1998 or 1 altitude iite 1992 at the onset found with shell buried in of experiment aperture applied the soil to the mud surface and Road ditch Young 1998 200 187 13 7 7 280 m snails 1999 200 192 8 4 0 Adults 1998 120 120 0 1999 120 120 0 Road ditch Young 1998 200 170 30 15 0 820 m snails 1999 200 167 26 13 0 Adults 1998 120 110 10 8 3 1999 120 113 7 5 87 1 Young snails 1 2 mm in height Adults 4 to 6
13. nails when the area was covered with water again unpubl data To explain these diffe rences the following questions have arisen has the al titude of sites and consequently local climatic condi tions an influence on the ability of G truncatula to aestivate Do the shell heights of surviving snails show any fluctuations in relation to altitude Do the snails from lowland or highland populations aestivate by burrowing into the substratum To answer these questions three experiments were carried out in the field and the laboratory on 11 French populations of G truncatula living in highland and lowland stations 2 Material and methods 2 1 Snails studied The six lowland populations of G truncatula are li ving in the department of Haute Vienne central Fran ce and inhabit peripheral extremities of open drainage furrows in swampy meadows 4 sites or road ditches 2 sites All these habitats are located within a 10 km radius around the town of Bellac and their altitude ranges from 206 to 282 m The five highland popula tions are located in the department of Puy de D me in the Massif Central and also colonize open drainage furrows in meadows 3 sites or road ditches 2 sites These last stations are located in the communes of Bromont Lamothe Pontgibaud and Saint Ours and their altitude ranges from 806 to 900 m The geogra phic distance between the former stations and the latter sites is 160 km The subsoil
14. r Mollusque vecteur de Fasciola hepatica Linn Tr matode en fonction de l altitude des prairies Th se Doct M d V t Lyon n 20 92 p De Massias E Rondelaud D Mage C amp Gevrey J 1996 Lym naea truncatula Miiller une seule g n ration annuelle dans les prairies d estive du Jura et des Alpes Bull Soc Fr Parasitol 14 54 61 Goumghar M D 2000 Recherches cologiques thologiques et parasitologiques sur des populations marocaines et frangaises de Galba truncatula Mollusca Doctorat Th se Univ de F s Ma roc 270 p Kendall S B 1949 Bionomics of Limnaea truncatula and the parthenitae of Fasciola hepatica under drought conditions J Hel minthol 23 57 68 Mehl S 1932 Die Lebensbedingungen der Leberegelschnecke Galba truncatula Miiller Untersuchungen iiber Schale Verbrei tung Lebensgeschichte nat rliche Feinde und Bekampfungsm6 glichkeiten Arb Bayer Landesanst Pflanzenbau Pfanzenschutz 2 1 177 7 ALTITUDE AND AESTIVATION OF GALBA TRUNCATULA 217 Moukrim A amp Rondelaud D 1992 Vertical spatial behaviour patterns of Lymnaea truncatula in relation with origin of snails infection with Fasciola hepatica and experimental environment Ann Parasitol Hum Comp 67 174 179 Peters B G 1938 Habitats of Limnaea truncatula in England and Wales during dry seasons J Helminthol 16 213 260 Roberts E W 1950 Studies on the life cycle of Fa
15. sciola hepati ca Linnaeus and of its snail host Limnaea Galba truncatula Miiller in the field and under controlled conditions Ann Trop Med Parasitol 44 187 206 Rondelaud D amp Morel Vareille C 1975 Distribution estivale et survie des Limn es tronqu es Lymnaea Galba truncatula M l ler saines ou infest es par Fasciola hepatica L Ann Parasitol Hum Comp 50 603 616 Smith G 1981 A three year study of Lymnaea truncatula habi tats disease foci of fascioliasis Br Vet J 137 398 410 STAT ITCE 1988 Manuel d utilisation Institut technique des c r ales et des fourrages Service des tudes statistiques Boigne ville France 210 p Vareille Morel C Dreyfuss G amp Rondelaud D 1999 The cha racteristics of habitats colonized by three species of Lymnaea Mollusca in swampy meadows on acid soil their interest for control of fasciolosis Ann Limnol 35 173 178
16. ter were finally poured in each breeding box to flood dried substratum and to re activate buried snails 2 3 Parameters studied The alive G truncatula were recognized from dead snails by the presence or the absence of a reaction after the pinch of a tentacle under the stereomicroscope The parameters studied in the first investigation we re the numbers of G truncatula noted during the first or the third count the corresponding survival rates and the shell height of surviving snails In the second investigation they were the numbers of live snails which left dried soil samples after their flooding with water the height of their shells and the durations of snail re activation in water Lastly in the third investi gation the numbers of snails buried into the mud and the corresponding percentages were studied Individual values for the shell heights in the first in vestigation and for each parameter studied in the se cond investigation were averaged and standard devia tions were established taking into account the parame ter the site studied and the year of investigation Com parison test of experimental frequencies and one way analysis of variance Stat Itcf 1988 were used to esta blish levels of significance 3 Results Table 1 gives the results recorded in the 49 ditch areas during summer drying In open drainage furrows as well as in road ditches the survival rates of G trun catula after flooding were signific
17. terr es dans le sol en dess chement sont plus lev s en altitude 13 et 15 des juv niles par exemple au lieu de 4 et 7 7 en plaine Chez ces derni res populations seuls les jeunes mollusques s enterrent alors que 5 8 et 8 3 des adultes en altitude s enfouissent par tiellement Le climat local des sites tudi s et l aptitude des mollusques s enterrer dans le sol avant la disparition de l eau stag nante en juillet peuvent expliquer la survie plus lev e des limn es pendant l estivation 1 Facult des Sciences Universit Sidi Mohamed Ben Abdallah B P n 1796 30 000 F s Atlas Morocco 2 UPRES EA n 3174 Facult s de M decine et de Pharmacie 2 rue du Docteur Raymond Marcland 87025 Limoges Cedex France Article available at http www limnology journal org or http dx doi org 10 1051 limn 2001018 212 M D GOUMGHAR M RONDELAUD G DREYGUSS M BENLEMLIH 2 1 Introduction The snail Galba truncatula O F M ller is capable of survival throughout a considerable period of drought i e more than a year under laboratory conditions Ken dall 1949 In the field the aestivation of this species decreases in length with increasing altitude as it ranges between 4 and 8 weeks in central France below 300 m Rondelaud amp Morel Vareille 1975 between 3 and 6 weeks in the Jura at 800 1 200 m and does not exist in the Alps between 1 800 and 2 600 m de Mas sias et al 1996 Consequently the number
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