Observations on the reproductive period of the freshwater mussel Potomida littoralis (Unionidae)

2004·4.5 MB·English

by  Karl-Otto Nagel

SociedadEspañola deMalacología Iberus, 22 (2): 1-8, 2004
Observations on the reproductive period of the freshwater
mussel Potomida littoralis (Unionidae)
Observaciones sobre el periodo reproductor del mejillón de agua
dulce Potomida littoralis (Unionidae)
NAGEL*
Karl-Otto
Recibidoel17-XII-2003.Aceptadoel5-II-2004
ABSTRACT
Data on the occurrence of gravid Potomida littoralis are presented from museum collec-
tions, field samplings and published literatura. Gravid animáis and released glochidia are
recorded to occur between March and October. The smallest gravid animáis were four or
five years oíd. The length of the brooding period apparently follows a latitudinal cline.
Potomida littoralis is most likely a tachytictic consecutive brooder with unsynchronised
broods.
RESUMEN
Se aportan datos sobre la presencia de ejemplares grávidos de Potomida littorales, a par-
tir de colecciones de museos, muéstreos de campo y bibliografía. Los reproductores y la
liberación de gloquidios se produce entre marzo y octubre. Los reproductores menores
eran animales de cuatro o cinco años de edad. La duración del periodo de cría sigue, en
apariencia, una tendencia latitudinal. Potomida littoralis se reproduce en primavera y en
verano, con puestas no sincronizadas.
KEYWORDS: Reproduction, Mollusca,Potomidalittoralis, Unionidae
PALABRAS CLAVE: Reproducción, moluscos,Potomidalittoralis, Unionidae.
INTRODUCTION
Freshwater mussels (Unionoida) are Bauer, 1988; Young, Cosgrove and
facedwithaserious declineinboththeir Hastie, 2001; Unió crassus: Hochwald,
numbers and distribution inmany parts 2001; Pseudunio auricularius (syn: Mar-
of the world (Bogan, 1993). Reproduc- garitifera auricularia): Araujo and
tion biology and ecology of juvenile Ramos, 2001). The biology and ecology
mussels are key factors that determine of most other European species remain
the survival abilities of freshwater insufficientlyknown.
mussel populations (Bauer, 2001). The occurrence of Potomida littoralis
Several species occurring in Europe that (Cuvier, 1798) (authorship of this taxon
are more seriously threatened have according to Falkner, Bank and von
received considerable attention in the Proschwitz, 2001 and Falkner, Ripken
past decades (Margaritifera margaritifera: and Falkner, 2002) continúes to be
podhrádzou 3011, SK- 90001 Modra (Harmonía), SlovenskaRepublika- Slovakia. [email protected]
Iberus, 22 (2), 2004
Figure 1. Orientation map forlocalities fromTableI. F: France; E: Spain; P: Portugal;TR:Turkey;
SYR: Syria; IL: Israel.
Figura 1. Mapadelaslocalidadesdela TablaI. F:Francia;E:España;P:Portugal; TR: Turquía;SYR:
Siria;IL:Israel.
widespread in Western Europe (France, bly determined the sex of these speci-
Spain, Portugal), however for other mens by histological studies but this is
parts of the species' distribution range not stated explicitly in his paper. His
(Greece, Turkey, Near and Middle East, findings however suggest that Potomida
Northern África) no information is cur- littoralisisdioeceous.
rently available. Data on the general bi- This paper is a report on the occur-
ology ofthis species datebackto thebe- rence of gravid specimens ofP. littoralis
ginning of the last century. Haas (1917) in the river Ognon (eastern France) and
discovered thatthe species has 4 marsu- on the presence of gravid mussels and
pial gills (= tetrageny). He examined the glochidia of this species based on pub-
anatomyofa singlemalespecimenfrom lished data and museum material. The
France and 11 males and 3 sterile (= data is culled from three distinct áreas
non-gravid) females ofRhombunio rothi withinthespecies' distributionrange.
Bourguignat, 1863 from Jaffa/Tel Aviv,
Israel (Haas, 1920). Later, he considered
this species tobe a synonym ofPotomida MATERIALANDMETHODS
littoralis (Haas, 1969). It mightbe noted
that the material of R. rothi studied by Sampling localities and collection
Haas should still be present in the dates are given in Table I. All localities
Senckenberg Museum, Frankfurt/M., are shown on an orientation map (Fig.
Germany. Lotn. SNF 000811 contains 25 1). Data on gravid specimens were
specimens preserved in alcohol, none of obtained from examination of the fol-
which are gravid. The label reads: lowingcollections:
"Rhombunio rothi (Bgt) - Jaffa - J. Aha- 1. Collection Kinzelbach, University
roni S. 1913". Haas (1924) later exam- of Rostock, Germany (Prof. Dr. R.
ined the condition ofthe marsupial gills Kinzelbach). Reference numbers in
ofanimáis collected in Spain. He proba- TableII:VO-78/
NAGEL: Reproductive period ofthe freshwatermussel Potomida littoralis (Unionidae)
TableI. Listoflocalities.
TablaI. Listadelocalidades.
Riveror River Departmement,
No. Samplinglocality
stream basin Province,country
France
1 Cirey-les-Bellevaux, 19kmNNEofBesangon Ognon Rhóne Haute-Saóne
2 Marnay,ca20kmWNWofBesangon Ognon Rhóne Haute-Saóne
3 canalnearMontfrin, 20kmWSWofAvignon Gardon Rhóne Gard
4 Clerey, 13kmSEofTroyes Seine Seine Aube
5 leGuétin,about1,5kmupstreamofconfluencewithLoire, Allier Loire Nievre
9kmSWofNevers
6 Brehemont,27kmWNWofTours Indre Loire Indre-etLoire
7 Candes-St.Martin,50kmWNWofTours Vienne Loire Indre-etLoire
8 Chauvigny,9kmEofPoitiers Vienne Loire Vienne
SpainandPortugal
9 LakeofBañolas/Banyoles,ca16kmNNWofGeron/Girorici endorheic Girona
10 Acequia (ditch)deSanAdrián,ca44kmESEofLogroño Ebro Navarra
11 Zaragoza CanalImperialdeAragón Ebro Zaragoza
12 Sástago,app. 56kmSEofZaragoza Ebro Ebro Zaragoza
13 nearRuidera,ca26kmSSEofTomelloso LagunasdeRuidera Guadianai AlbaceteandCiudadReal
14 Goyán/Goián, 12kmupstreamoftherivermouthat Miño Miño Pontevedra
LaGuardia/AGuarda (at3differentbutveryciósesites)
15 nearVilaNovadeCerveira (oppositeofGoyán), Minho Minho VianadoCastelo,Portugal
ca12kmupstreamoftherivermouth
16 Tuy/Tui, 27kmupstreamoftherivermouth Miño Miño Pontevedra
17 SalvaterradoMiño, 39kmupstreamoftherivermouth Miño Miño Pontevedra
Turkey, SyriaandIsrael
18 nearSamandaj,ca25kmSWofHatay(Antakya) Orantes Orantes Hatay,Turkey
19 (1) confluenceofthetwooutletsoftheLakeofHoms Orantes Orantes Syria
(Buhairatal-QattinaorB.al-Hims) and (2) backwater
20 atbridgeofroadHoms-Tartus Orantes Orantes Syria
21 stagnantbackwaterintheal-GhabENEofAinal-Kurum Orantes Orantes Syria
22 canalatcrossingoftheroadAinal-Kurumto Orantes Orantes Syria
Saqalibiya (Sqelbié)
23 LakeTiberias(Kinneret) Jordán Israel
2. Collection of recent freshwater Live adult mussels were gently opened
invertebrates at the Museo Nacional de byhand to approximately 1 cm. The soft
Ciencias Naturales, Madrid, Spain. Ref- paíts of most museum specimens were
erencenumbersinTableII: MNCNFW- alreadyremoved fromthe shell and sep-
3. Senckenberg-Museum, Frankfurt arately stored. It is important to remem-
am Main, Germany. Reference numbers ber that in Potomida littoralis the inner
inTableII: SNF- and outer gills become filled with eggs.
Gills of living or preserved speci- In this case they are swollen and non-
menswereinspectedtoseewhetherthey transparent. Filled marsupia are cream
were filled. The developmental status of white to light brown in live animáis,
the content of the gills was not always whileunfilled gills aresemi-transparent,
determined and is not reported here. thinandgreyishcolour.
Iberus, 22 (2), 2004
Mussels from the river Ognon at tial observations and the lack of distinc-
Cirey-les-Bellevaux were repeatedly tionbetween individual and population
inspected by hand while wading on the behaviour have prevented us from
riverbanks. The máximum depth detecting the actual patterns until
sampled was 1.5 m. Sampling dates are recently (Heard, 1998). Specific infor-
given in Table III. The mussels were mation on the reproductive period of
painted with numbers for individual Potomida littoralis is scattered. The only
recognition and measured to the nearest published records of gravid animáis are
1/10mmwithaveneercalliper. from Haas (1917, 1920) and Prashad
(1919).
Haas (1917) conducted regular sam-
RESULTS plingsbetweenJuly 18andSeptember5,
1916 in the river Ebro at Sástago. He
Table II reports the findings from found individuáis carrying eggs and
collections and field observations. All larvae at the beginning of this period
gravid specimens were encountered and he recognized freshly metamor-
fromApriltoOctober. phosed mussels on the last date.
The smallest gravid specimen was However, Haas obviously failed to
mm
39.3 in length (June 6, 1990, river account for the presence of gravid
Miño at Goyán). The smallest gravid animáis in a sample he had taken the
mussel from the Ognon measured 41.0 year before (September 7-8, 1915; Haas
mm (Table III). In both cases, three, 1916). A small proportion of those
perhaps four, darkly coloured growth mussels, still preserved in the Sencken-
lines were evident on the outside of the berg Museum, are gravid (Table II). For
shell. This means that the animáis were the other samples carried out in 1916
in their fourth (or fifth) spring/summer (Sástago:August15,22,29,September5;
periodwhentheyreproduced. Gallur, ca 42 km NW of Zaragoza: Sep-
Table III reports the findings of re- tember 3) Haas didnot give thenumber
peated observations of marked individ- of P. littoralis collected. It remains
ual mussels in one locality in eastern unclear whether he inspected them for
mm
France. Mussel with length 55.3 gravidityatall.
was not found gravid in the year 2000 Prashad (1919) made observations
andbecamegravidin2001. Sincethean- on 3 specimens of Unió (Rhombunio)
imal was among the largest in that pop- semirugatus collected inOctober, 1912,in
ulation it was most likely also sexually Lake Tiberias (Sea of Galilee). The
mature in the first year of observation. species ñame is considered by Haas
This individual may have paused from (1969) to be a synonym of Potomida lit-
reproductionin2000 ormayhaverepro- toralis. One mussel was gravid in the
ducedexceptionallylateinthatyear. sample of Prashad. Apparently, it con-
Excluding animáis that are less than tained glochidia only in the outer gills.
39.3 mm, which was the size of the In fact, Prashad regarded the outer gills
smallest gravid individual, the number as the only structure having marsupial
of mussels found gravid in the river function (= ectobranchy). Apart from
Ognon was 33%. Similar valúes were the presence of larvae, Prashad based
found for the pooled samples from the his identification of marsupial gills on
river Orontes (33%) and the Ebro at the spacing of the gilí septa. Haas
SástagoonJuly18, 1916 (30%). (1924) expressed doubts aboutthevalid-
ity of this interpretation since he identi-
fied four marsupial gills in Rhombunio
DISCUSSION rothi by histological examinations
(Haas, 1920, 1924). Considering all
Little is known about the brood observations reported in Table II, it
behaviour of unionoidean bivalves. In might be concluded that the specimen
many cases inferences from circumstan- of Prashad was collected at the end of
NAGEL: Reproductive period ofthe freshwatermussel Potomida littoralis (Unionidae)
Table II. Observations on the brooding behaviour ofPotomida littoralis. The number ofgravid
mussels when present is given in parenthesis after the sample size. Live glochidia: data from
ARAUJO, BRAGADOAND RAMOS (2000).Abbreviations. ?: numbernotspecified.
TablaII. ObservacionessobreelcomportamientodecríadePotomidalittoralis. Elnúmero deejempla-
res reproductoresseda entreparéntesis tras eltamaño de muestra. Gloquidios vivos: datos tomados de
Araujo, BragadoyRamos (2000).Abreviaturas. ?: númerosinespecificar.
Month Live Gravid Samplesize 1Mo.ofsampling Date Reference
glochidia mussels locality(fromTable1)
January No1
February Nodata No 2 18 26.2.2001 MNCNFW-681
March Yes2 No 21 11 5.3.1915 Haas,1916;SMF003052
April Yes No 6 14 16.4.1991 MNCNFW-691
No 9 1 23.4.2000 thisstudy,seeTableIII
Yes 10(3) 1 29.4.2001 thisstudy,seeTableIII
May Yes
June Yes Yes 3(1) 15 6.6.1990 MNCNFW-640
Yes 36(9) 1 10/11.6.2000 thisstudy,seeTableIII
Yes "several" (4) 2 23.6.2000 thisstudy
Yes 6(2) 1 23.6.2000 thisstudy,seeTableIII
No 20 7 30.6.1991 NagelandBadino,2001
No 18 6 30.6.1991 NagelandBadino,2001
July Yes No 33 4 1.7.1991 NagelandBadino,2001
Yes KD 10 11.7.1996 MNCNFW-1157
No 7 14 11.7.1990 MNCNFW-645
Yes "severalhundred" (?) 12,at0-0.5m 18.7.1916 Haas,1917,1920;SMF003054;
sub-sample:47 (14) depth thisstudy
No 5 5 21.7.1985 NesemannandNagel,1989
No 3 6 23.7.1985 NesemannandNagel,1989
No 4 7 24.7.1985 NesemannandNagel,1989
No 2 8 26.7.1985 NesemannandNagel,1989
August Yes Yes "many'" (2)at0-0.5m,"some" 12 2.8.1916 Haas,1917;Haas, 1920
(all?)at5-6mdepth
No 6 21 3.8.1978 V0-78/12
Yes morethan1 (1) 22 3.8.1978 V0-78/12a
Yes 8(4) 23 5.8.1978 V0-78/20
Yes 17(6) 24and25 8/10.8.1978 V0-78/28;V0-78/29
No 8 18 4.8.1988 MNCNFW-1295
Yes ?at -0.5m,?(all?) 12 8.8.1916 Haas, 1917
at6mdepth
Yes 9(2) 20 23.8.1978 V0-78/49
No 2 14 28.8.1990 MNCNFW-652
September Yes Yes sub-sample:35(5) 12 7/8.9.1915 SMF323165;thisstudy; (Haas,1916)
No 42 12 8.9.1915 Haas,1916;SMF003053
No 14 13 8.9.2000 MNCNFW-1500
No 1 19 11.9.2002 MNCNFW-1543
No 10 9 15.9.1914 SMF003049
No 5 14 18.9.1990 MNCNFW-654
October Yes3 Yes 3(1) 23 October1912 Prashad,1919
No 17 3 5.10.1989 NagelandBadino,2001
No 19 17 7.10.1988 NagelandBadino,2001
No 1 16 24.10.1989 MNCNFW-498
November Nodata No 2 14 6.11.1990 MNCNFW-664
No 1 18 6.11.1990 MNCNFW-665
December No
7fourdatesin1998;2from6.3.1997;3untíl9.10.1997
Iberus, 22 (2), 2004
Table III. Observations ofthe reproductive status ofPotomida littoralis in the river Ognon near
Cirey-les-Bellevaux, France. From a total of37 individually marked animáis only those are listed
thatcouldbe inspectedatleasttwotimes.The remaindingoneswerenotgravidonApril 23, 2000
(1 specimen) or onJune 10 - 11, 2000 (12 specimens). Length ofspecimens as measured on day
offirstrecord. No intensivesamplingonJune23, 2000.
TablaIII. Observacionesdelestatus reproductordePotomida littoralis en elrío Ognon cercade Cirey-
les-Bellevaux, Francia. Deun totalde37especímenesmarcadossóloseincluyenaquellosqueseobserva-
ron almenosdos veces. Los restantes no estaban en estado reproductorel23 deabrilde2000 (1 ejem-
plar)oel10-11 dejuniode2000(12ejemplares). Sedalalongitudtomadaeldíadelaprimeraobser-
vación. Noserealizóun muestreointensoel23dejuniode2000.
Length Gravki Length Gravid
(mm) 2000 2001 (mm) 2000 2001
April23 June10/11 June23 April29 April23 June10/11 June23 April29
27.8 - - 47.0 - + -
30.2 - - 47.7 +
39.0 - - 48.1 - -
39.4 - - 48.2 +
40.0 - 49.3 + +
41.0 - + 50.2 -
41.8 + 51.5 + -
44.6 + + 51.7 +
45.6 - 54.7 - - -
46.6 - - 55.3 - - - +
46.7 + 58.7 +
46.8 - 65.9 - t
Explanationofsymbols:+ gravid,- nol.gravid,t dead,noentry:notfound.
the gravidity period and had already No gravid mussels were found in
expelled the content of the inner gills France in the 64 specimens sampled in
thus giving the appearance of an ecto- July and October. Several explanations
branchousstate. are possible for this, for example, lati-
Based on the observations of Haas tude. It may be safe to assume that the
(1920, 1924), Nagel (1988, p. 3, fig. 1) reproductive season for P. littoralis is
hypothesized that Potomida littoralis is a abbreviated at higher latitudes where
summer breeder, i.e. tachytictic like the periods with water temperatures
Europeanspecies ofthe genus Unió. The favourable for the growth of food parti-
observations from the river Ognon cles (bacteria, algae) are short. There is
(Table III) fit well into this pattern. evidence that at least some unionoid
Recently,Araujo, BragadoandRamos species allocate only surplus energy to
(2000) reported on live glochidia (valves reproduction (Hochwald, 2001 and ref-
with soft body) in drift net samples erences therein). Alternative explana-
from early March to beginning of tions are population specific and would
October, 1997, in the Canal Imperial de pointto ahighparasiteload andnatural
Aragón that takes water from the Ebro or anthropogenic habitat disturbances.
(sampling localities near the villages of All these factors can induce individuáis
Grisén and Alagón, between Gallur and or entire populations to suppress repro-
Zaragoza, see Table II). These data duction. This latter phenomenon was
confirm the tachitixis but also give evi- previously described for some species
dence of a very long reproductive (Margaritifera margaritifera: Bauer, 1987;
period. Ross, 1992; Unió crassus: Hochwald,
,
NAGEL: Reproductive period ofthe freshwater mussel Potomida littoralis (UnionidaeJ
2001; Hyridella depressa: Walker, Byrne, with probably consecutive unsynchro-
HlCKEYANDROPER,2001). nised broods. The reproductive period
The apparently very long reproduc- can span from March to October. More
tive period in the southern locations data are needed to determine if the
makes consecutive breeding (more than length of the reproductive period
onebrood inthe reproductiveperiod) of follows alatitudinalcline.
the species quiteprobable,butpresently
there is no direct evidence for this. This
ACKNOWLEDGEMENTS
form of reproductive behaviour,
however, seems to be widespread
amongunioniodmussels (Heard, 1998). R. Araujo and R. Kinzelbach pro-
Amean of 30% gravid mussels was vided information on collectionmaterial
found in the samples from the Ognon, and E.M. Nagel assisted the field sam-
one sample from the Ebro and the plings. The manuscript benefited from
pooled Orontes samples (Table II). comments provided by a referee and by
Assuming a sex ratio of 1:1 would mean R. Araujo and J. Plant, the latter who
that one-third of the females did not edited my English. To all of them I
actively particípate in reproduction at remain most grateful. The study of the
the times ofsampling. This patternindi- collection in Madrid was supported by
cates unsynchronised breeding within a the Museo Nacional de Ciencias Natu-
population. rales and by a grant from the European
From the above it is concluded that Commission's Human Potential Pro-
Potomida littoralis is a tachyticticbrooder gramme.
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