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Low genetic differentiation between two morphotypes of the gastropod Nacella concinna from Admiralty Bay, Antarctica

DOI:10.4202/ppres.2010.11
Authors:
Katarzyna Joanna Chwedorzewska at Warsaw University of Life Sciences - SGGW
Katarzyna Joanna Chwedorzewska
Małgorzata Korczak-Abshire at Institute of Biochemistry and Biophysics Polish Academy of Sciences
Małgorzata Korczak-Abshire
Piotr T Bednarek at Instytut Hodowli i Aklimatyzacji Roslin
Piotr T Bednarek
Marta Potocka at Polish Academy of Sciences
Marta Potocka
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Abstract

During laboratory and field experiments on Nacella concinna on the west coast of Admiralty Bay, King George Island (Antarctica) clear morphological and behavioural differences between two limpet forms (N. concinna polaris and N. concinna concinna) were found. They suggested presence of genetic divergence. AFLP (amplified fragment length polymorphism) profiling of N. concinna individuals representing the two forms revealed nearly 32% of polymorphic bands; only 2% of them differed between the forms. Our results suggest that the observed phenotypic variation seems to be a result of adaptation to environ− mental conditions and not of any genetic divergence.
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Low genetic differentiation between two morphotypes
of the gastropod Nacella concinna from Admiralty Bay,
Antarctica
Katarzyna J. CHWEDORZEWSKA1, Małgorzata KORCZAK1, Piotr T. BEDNAREK2
and Marta MARKOWSKA−POTOCKA1
1Zakład Biologii Antarktyki PAN, Ustrzycka 10/12, 02−141 Warszawa, Poland
<kchwedorzewska@go2.pl>
2Instytut Hodowli i Aklimatyzacji Roślin, 05−870 Warszawa – Radzików, Poland
Abstract: During laboratory and field experiments on Nacella concinna on the west coast
of Admiralty Bay, King George Island (Antarctica) clear morphological and behavioural
differences between two limpet forms (N. concinna polaris and N. concinna concinna) were
found. They suggested presence of genetic divergence. AFLP (amplified fragment length
polymorphism) profiling of N. concinna individuals representing the two forms revealed
nearly 32% of polymorphic bands; only 2% of them differed between the forms. Our results
suggest that the observed phenotypic variation seems to be a result of adaptation to environ−
mental conditions and not of any genetic divergence.
Key wo rd s : Antarctica, Nacella concinna, genetic diversity, AFLP.
Introduction
Herbivorous gastropod Nacella concinna is a characteristic representative of
the Maritime Antarctic benthos. It occurs in two forms: N. concinna polaris and
N. concinna concinna (Berry and Rugge 1973; Branch and Branch 1981). Mor−
phological and behavioral differences between these two forms were observed by
many authors (Nolan 1991; Markowska and Kidawa 2007; de Aranzamendi et al.
2008). N. concinna polaris occurs on stony bed rock in the littoral zone, and
N. concinna concinna is present in the sublittoral and in the intertidal zones below
4 m down to 110 m depth (Walker 1972; Berry and Rugge 1973; Castilla and
Rozbaczylo 1985; Nolan 1991) along the Antarctic Peninsula and adjacent islands
(Picken 1980). The intertidal morphotype has a taller and heavier shell as com−
pared to the rock pool morphotype having a lighter and flatter shell (Powell 1951;
Nolan 1991). These two morphotypes also differ in important physiological traits
(Waller et al. 2006; Weihe and Abele 2008).
Pol. Polar Res. 31 (2): 195–200, 2010
vol. 31, no. 2, pp. 195–200, 2010 doi: 10.4202/ppres.2010.11
In previous studies limpets Nacella concinna were gathered from rock pools
during the low tide and by divers from the subtidal area at the depths of 5–8 m.
Limpets collected from rock pools were significantly smaller than the subtidal
individuals (ttest, P< 0.005), ranging from 19.8 to 43.3 mm shell length (mean
= 21.2, SE = 0.32 mm, n= 222), in comparison to 23.7–47.0 mm (mean = 37.4,
SE = 0.49, n= 191) for the subtidal ones. Visible difference in reaction to preda−
tors was also noted between the two described limpet populations in laboratory
and field experiments (Markowska and Kidawa 2007; Markowska 2008).
The aim of this study was to explore the genetic relationships between the two
forms described above: the rock pool N. concinna polaris and the subtidal N.
concinna concinna form from the Admiralty Bay.
Material and methods
DNA extraction. — Samples were collected during the previous experiment
run by Markowska (2008). Forty eight individuals from both forms were taken for
the AFLP analysis. DNA was extracted from about 20 mg of tissue, stored in 70%
ethanol. Samples were dried on Watman paper, then followed overnight proteinase
K digestion. Next steps of extraction followed the manufacturer’s protocol recom−
mendation (NucleoSpin®Tissue, Macherzy−Nagel, AQUA LAB). Purity and quan−
tity of the samples were determined spectrophotometrically. DNA integrity and lack
of RNA impurities were tested by agarose gels electrophoresis (1 × TBE buffer with
0.5 μg/ml ethidium bromide at 20 V/cm).
AFLP analysis. — The AFLP technique was performed according to the previ−
ously described procedures with minor modifications (Chwedorzewska et al. 2006).
Briefly, 250 ng of genomic DNA was digested simultaneously with two restrictive
enzymes EcoRI and MseI. This was followed by ligation of the appropriate adaptors,
preselective and, finally, selective amplification steps (core sequence Table 1). For
196 Katarzyna J. Chwedorzewska et al.
Table 1
Adapter and primer sequences
Adapter/Primer code Sequence (5’−>3’)
Adapter EcoRI CTCGTAGACTGCGTACC
CATCTGACGCATGGTTAA
Adapter MseITACTCAGGACTCATA
GAGTCCTGAGTAGCAG
EcoRI preselective primer GACTGCGTACCAATTCA
MseI preselective primer GATGAGTCCTGAGTAAC
E−Azz − selective primer GACTGCGTACCAATTCAzz
M−Cyy − selective primer GATGAGTCCTGAGTAACyy
E and M are for any selective primer complementary to EcoRI and MseI adaptors respectively; −zz,
−yy − any combination of the nucleotides at the primers 3’ends.
the selective amplification seven primer pair combinations (EcoRI – AGG/MseI–
CAC, EcoRI – ACG/MseI – CAC, EcoRI – ACT/MseI – CGC, EcoRI – ACC/MseI
–CAC,EcoRI – AAA/MseI – CAG, EcoRI – AGT/MseI – CAA, EcoRI –
AAA/MseI – CGG) were used (Table 1). The EcoRI compatible primers were la−
belled at their 5’−ends with gamma – 32P ATP. PCR products were separated on 5%
PAGE and X−ray films were exposed to the gels at −70°C overnight.
Data analysis and statistics. — Reproducible (experiment was run twice), in−
dividual AFLP fragments were scored as either present (1) or absent (0). Their fre−
quencies were calculated for all the markers. Xlstat v.7.5.2 excel add−in software
(www.xlstat.com, Addinsoft) was used to perform clustral analysis (Aggregation
criterion: unweighted pair−group average UPGMA, Jaccard coefficient of dissimi−
larity) and construct the dendrogram. Principal Component Analysis (PCA) and
Analysis of Molecular Variance (AMOVA) was carried out using GeneAlex5.1
excel add−in software (Peakall and Smouse 2001).
Results and discussion
DNA profiling of the samples representing animals collected from rock pools
and from subtidal zone revealed 374 scoreable fragments amplified by seven
primer pair combinations. The number of the DNA fragments generated by an in−
dividual primer pair varied from 31 to 72 with an average of 53. In total all primer
pairs generated 121 (32% of all signals) polymorphic fragments with an average of
17 per primer combination (Table 1).
Clustral and PCA analyses using all the polymorphic bands failed to differentiate
among all samples collected from rock pools and from subtidal. Nevertheless, the first
main axis of the PCA explained 88.00% and the second 4.34% of the identified vari−
ability (Fig. 1). Based on the mentioned methods samples were randomly distributed
and formed no separate groups. The similarity matrix was analysed using UPGMA.
Dendrogram was based on all DNA fragments obtained with seven selective primer
pairs for all individuals. Cluster analysis did not reveal any groups (the results of both,
cluster and PCA analysis were similar, thus only PCA diagram is presented).
Although molecular profiling of N. concinna individuals revealed nearly 32%
of the polymorphic bands, few (2%) were discriminated between the analyzed
populations as demonstrated by AMOVA (Table 2).
Genetic diversity of Nacella concinna 197
Table 2
Results of AMOVA of N. concinna samples from all analysed populations. Significance
tested by a permutation analysis against alternative random partitioning of individuals
(999) across populations.
Source of variation df SS Estimate variance Total variance (%) P−value
Among populations 1.0 5.312 0.066 1.7 <0.001
Within populations 46.0 172.001 3.739 98.3 <0.001
Genetic differentiation of the two forms was studied by de Aranzamendi et al.
(2008) with use of ISSR−PCR markers and indicated that the two analyzed forms
can be considered as genetically distinct populations maintaining low levels of
gene flow. Our results, obtained by a different genetic method focused on total
genomic DNA, showed much smaller differences between the analyzed forms (ac−
cording to AMOVA less than 2%) and did not confirm results of de Aranzamendi
et al. (2008) study. These differences may be linked to too small sample size taken
for analysis by de Aranzamendi (only eleven individuals per population).
Thus, our results may point to specificity of this species reproduction physiol−
ogy. Nacella concinna produces and disperses long−lived planktonic larvae, which
can survive for two months in the water column (Bowden et al. 2006). The pelagic
198 Katarzyna J. Chwedorzewska et al.
Fig. 1. Principal Component Analysis (PCA) of two population of Nacella concinna collected from
rockpools (A) and from subtidal zones (B), based on AFLP data.
long−lived larvae are able to colonise new sites rapidly, thus recruitment occurs
within a common gene pool and there is little opportunity for local genetic diver−
gence. In N. concinna the reproduction takes place about 3 weeks after the water
temperature exceeds −1.4°C (Picken 1980, Picken and Allan 1983). Thus spawn−
ing appears to be synchronized with the increasing temperature and probably the
availability of food (Brathes et al. 1994). However, it does not seem to be a suffi−
cient barrier to avoid gene exchange in form of partial reproductive isolation.
Moreover, the intertidal morphotype (equivalent of rock pool in presented study)
is also migratory, moving seasonally between the intertidal and subtidal zones
(Walker 1972). Probably these phenotypic and behavioural variations (Mar−
kowska 2008), specific to these populations, might be the result of phenotypic
plasticity expressed in particular environmental conditions, rather than it reflects
genetic differences. The heterogeneous environment that characterises intertidal
region (different wave exposures, temperature, ultraviolet irradiation and variable
chemical−physic parameters over a short vertical distance, different predators)
could be responsible for such a significant morphological variability.
Acknowledgments. — We would like to thank two anonymous reviewers for constructive
advice that has improved our paper.
References
DE ARANZAMENDI M.C., SAHADE R., TATIA'N M. and CHIAPPERO M.B. 2008. Genetic differentia−
tion between morphotypes in the Antarctic limpets Nacella concinna as revealed by inter−simple
sequence repeat markers. Marine Biology 154: 875–885.
http://dx.doi.org/10.1007/s00227-008-0980-5
BERRY R.J. and RUDGE P.J., 1973. Natural selection in Antarctic limpets. British Antarctic Survey
Bulletin 35: 73–81.
BRANCH G.M. and BRANCH M.L. 1981. Experimental analysis of intraspecific competition in an
intertidal gastropod, Littorina unifasciata.Australian Journal of Marine & Freshwater Re−
search 32: 573–589. http://dx.doi.org/10.1071/MF9810573
BRATHES J.C., FERREYRA G. and DE LA VEGA S. 1994. Distribution, growth and reproduction of the
limpet Nacella (Patinigera) concinna (Strebel 1908) in relation to potential food availability, in
Esperanza Bay (Antarctic Peninsula). Polar Biology 14: 161–170.
BOWDEN D.A., CLARKE A., PECK L.S. and BARNES D.K.A. 2006. Antarctic sessile marine benthos:
colonisation and growth on artificial substrata over 3 years. Marine Ecology Progress Series
316: 1–16. http://dx.doi.org/10.3354/meps316001
CASTILLA J.C. and ROZBACZYLO N. 1985. Rocky intertidal assemblages and predation on the gastropod
Nacella (Patinigera) concinna at Robert Island, South Shetland, Antarctica. Serie Cientifica del
Instituto Antártico Chileno 32: 65–73.
CHWEDORZEWSKA K.J., BEDNAREK P.T., LEWANDOWSKA R., KRAJEWSKI P. and PUCHALSKI J. 2006.
Studies on genetic changes in rye samples (Secale cereale L.) maintained in a seed bank. Cellular
and Molecular Biology Letters 11: 338–347. http://dx.doi.org/10.2478/s11658-006-0028-0
MARKOWSKA M. 2008. Reakcje ofiary na obecność drapieżnika, na przykładzie antarktycznych
ślimaków Nacella concinna z dwóch różnych siedlisk. Unpublished Ph.D. dissertation. Uni−
wersytet Gdański, Poland: 116 pp. (in Polish)
Genetic diversity of Nacella concinna 199
MARKOWSKA M. and KIDAWA A. 2007. Encounters between Antarctic limpets, Nacella concinna,
and predatory sea stars, Lysasterias sp., in laboratory and field experiments. Marine Biology
151: 1959–1966. http://dx.doi.org/10.1007/s00227-007-0633-0
NOLAN C.P. 1991. Size, shape and shell morphology in the Antarctic limpet Nacella concinna at
Signy Island, South Orkney Islands. Journal of Molluscan Studies 57: 225–238.
http://dx.doi.org/10.1093/mollus/57.2.225
PEAKALL R. and SMOUSE P.E. 2001. GenALEx V5: Genetic Analysis in Excel. Population genetic
software for teaching and research. Australian National University, Canberra http://www.
anu.edu.au/ BoZo/GenAlEx/
PICKEN G.B. 1980. The distribution, growth and reproduction of the Antarctic limpet NaceIla
(Patinigera) concinna (Strebel 1908). Journal of Experimental Marine Biology and Ecology 42:
71–85. http://dx.doi.org/10.1016/0022-0981(80)90167-7
PICKEN G.B. and ALLAN D. 1983. Unique spawning behaviour by the Antarctic limpet Nacella
(Patinigera) concinna (Strebel 1908). Journal of Experimental Marine Biology and Ecology 71:
283–287. http://dx.doi.org/10.1016/0022-0981(83)90121-1
POWELL A.W.B. 1951. Antarctic and subanctarctic Mollusca: Pelecypoda and Gastropoda. Discov−
ery Reports (USA) 26: 49–196.
WALKER A.J.M. 1972. Introduction to the ecology of the Antarctic limpet Patinigera polaris
(Hombron and Jaquinot) at Signy Island, South Orkney Island. British Antarctic Survey Bulletin
28: 49–71.
WALLER C.L., WORLAND M.R., CONVEY P. and BARNES D.K.A. 2006. Ecophysiological strategies
of Antarctic intertidal invertebrates faced with freezing stress. Polar Biology 29: 1077–1083.
http://dx.doi.org/10.1007/s00300-006-0152-3
WEIHE E. and ABELE D. 2008. Differences in the physiological response of inter− and subtidal Ant−
arctic limpets Nacella concinna to aerial exposure. Aquatic Biology 4: 155–166.
http://dx.doi.org/10.3354/ab00103
Received 21 October 2009
Accepted 28 April 2010
200 Katarzyna J. Chwedorzewska et al.
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  • Jun 2012
Seabirds and their response to climate pertur-bations are important bioindicators of changes in Antarctic ecosystems. During 30 years of observations of two chin-strap penguin (Pygoscelis antarcticus) colonies, one on King George Island and the other on Penguin Island (South Shetland Islands, Antarctica), the size of the breeding populations decreased by 84 and 41 %, respectively. We applied analyses of amplified fragment length polymor-phisms to study the genetic structure of the two populations and to evaluate the influence of the sudden population decrease. Our data indicate that there were only weak genetic differences between the populations, which were not strong enough to support the hypothesis of population differentiation. Weak genetic differences observed between the two populations seem not to be determined by selection processes. We hypothesize that the very low level of between-population genetic structure can be explained by some extent of genetic drift, which is largely compensated by gene flow. Moreover, the two populations seem to remain in a stationary state. Our results support the hypothesis of limited natal philopatry in chinstrap pen-guins. The observed decrease in population size is probably caused by emigration or a rise in juvenile mortality due to the increasing krill limitation of the marine food web. However, detailed research is required to address this issue.
KorczakChwedorzewska
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  • Mar 2013
Differences in the physiological response of inter- and subtidal Antarctic limpets Nacella concinna to aerial exposure
Article
Full-text available
  • Nov 2008
Antarctic intertidal zones are extremely harsh environments, and the Antarctic limpet Nacella concinna is one of the most conspicuous components of the macrofauna, colonizing such areas at King George Island, South Shetlands. The limpet subpopulation encompasses an intertidal and a subtidal ecomorph; these differ with respect to shell height and inner volume. We studied morphological, behavioural and physiological traits that distinguish both N. concinna subpopulations. We found a higher volume to circumference ratio of intertidal versus subtidal limpets to go along with a drastically reduced loss of body water during air exposure in intertidal specimens. Smaller intertidal limpets were less susceptible to desiccation than larger individuals. Further, the intertidal snails avoided accumulation of anaerobic metabolites (succinate, lactate and propionate), whereas subtidal limpets switched to anaerobic fermentation when exposed to air for > 12 h. Only acetate accumulated in both types of snails after 1.2 h. Mean pO(2) in shell water was higher in intertidal (2.6 kPa) than subtidal individuals (1.3 kPa) when submersed under water, and only the intertidal snails appeared able to respire air on emersion. These differences document strong physiological diversification between shore levels and shell morphs in the Antarctic limpet subpopulation at King George Island.
Ecophysiological strategies of Antarctic intertidal invertebrates faced with freezing stress
Article
Full-text available
  • Oct 2006
Recent studies have revealed a previously unanticipated level of biodiversity present in the Antarctic littoral. Here, we report research on the ecophysiological strategies adopted by intertidal species that permit them to survive in this environment, presenting cold-tolerance data for the widest range of invertebrates published to date from the Antarctic intertidal zone. We found significant differences in levels of cold tolerance between species within this zone. However, and contrary to expectations, intraspecific comparisons of subtidal and intertidal groups of eight species found significant differences between groups in only three species. One species, the nemertean Antarctonemertes validum, showed evidence of the presence of antifreeze proteins (thermal hysteresis proteins), with 1.4°C of thermal hysteresis measured in its haemolymph. We found a strong inverse relationship across species between mass and supercooling point, and fitted a power law model to describe the data. The scaling exponent (0.3) in this model suggests a relationship between an animal’s supercooling point and its linear dimensions.
Encounters between Antarctic limpets, Nacella concinna , and predatory sea stars, Lysasterias sp., in laboratory and field experiments
Article
Full-text available
  • Jan 2007
Antarctic limpets, Nacella concinna, from the Admiralty Bay (King George Island, South Shetlands) for at least part of the year (austral winter) co-exist with predatory sea stars Lysasterias sp. Our laboratory and field experiments established that the presence of Lysasterias sp. or its odour had considerable influence upon their behaviour. Limpets’ responses, consisting of shell mushrooming, shell rotation and flight, were distinctly different from their reaction to other stimuli, such as food and conspecific odours, or mechanical stimulation. Moreover, a significant impact of sea star presence on limpets’ activity was observed, with limpets fleeing to a distance of 60cm from the predator. Such reactions allow limpets to lower the incidence of sea star predation, but at the cost of presumptive disrupting of foraging and an additional energy expended for locomotion. A visible difference was noted between two limpet populations, with the rockpool limpets responding only after physical contact with being touched by a sea star, and the subtidal ones responding at a distance of up to 20cm.
Distribution, growth and reproduction of the limpet Nacella (Patinigera) concinna (Strebel 1908) in relation to potential food availability, in Esperanza Bay (Antarctic Peninsula)
Article
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  • Apr 1994
The present work addresses the effect of environmental factors (icing, water temperature, food availability) on the ecology of the patellid limpet Nacella (Patinigera) concinna, in a bay on the Antarctic Peninsula. Sampling was conducted at three depths (intertidal, 5m, 10m) from February 1987 to January 1988. Temperature was recorded and concentrations of Chlorophyll a were measured on the bottom, in the water and in the ice-water layer. The limpets were measured, weighed and a condition coefficient for somatic and gonadal mass was calculated. Their ages were estimated through size frequency distribution analysis and a seasonalized von Bertalanffy growth model was applied. The intertidal subpopulation migrated to deeper levels at the beginning of the icing season and recolonized the intertidal zone after ice retreat. The growth rate was very low (von Bertalanffy K 0.08). Growth rates showed important seasonal variations, with maxima during December and January. Nacella (P.) concinna spawns once a year and spawning coincided with raising water temperature (from -1.33C to-0.84C), and probably was also related to increasing spring food availability. Body mass increased during periods of high standing stock of microphytobenthos, revealing that ice-algae and phytoplankton were of minor importance as food sources for limpets in Esperanza Bay.
Genetic differentiation between morphotypes in the Antarctic limpet Nacella concinna as revealed by inter-simple sequence repeat markers
Article
Full-text available
  • Jun 2008
The limpet Nacella concinna (Strebel 1908) was the focus of numerous studies dealing with Antarctic benthos. One of the main characteristics of the species is the presence of two distinguishable morphotypes, one inhabiting the intertidal (during summer) and the other inhabiting the subtidal. For a long time these forms were considered as an expression of phenotypic plasticity, since previous studies did not found genetic differences between them. In the present work, we performed both a morphometric and a genetic differentiation analysis (using ISSR-PCR markers) of these two forms in three stations sampled at Potter Cove, South Shetland Islands. The results confirmed the morphological differences between intertidal and subtidal forms reported in other Antarctic localities. The genetic differences detected indicate that the two forms can be considered as genetically distinct populations maintaining low levels of gene flow. The degree of reproductive isolation of the ecotypes is discussed, as well as the possible origin of the divergence. The genetic differentiation observed can also have behavioral and physiological correlates, pointing out the importance of taking into account the potential differences in the response of both populations to different conditions in future studies in this species.
Introduction to the ecology of the Antarctic limpet Patinigera polaris (Hombron and Jacquinot) at Signy Island, South Orkney Islands
Article
  • Jan 1972
Natural selection in Antarctic limpets
Article
  • Jan 1973
Experimental analysis of intraspecific composition in an intertidal gastropod, Littorina unifasciata
Article
L. unifasciata dominates the upper levels of rocky shores at Cape Banks, New South Wales. Peak densities of up to 9600 m-2 occur near the centre of the littorine's vertical zonation and are associated with small body sizes. Density declines, and mean size rises, further down and more particularly further up the shore. Largest animals occur at the top of the shore and in areas experiencing strong wave action, where densities are low. Field experiments showed that increase in density results in a decrease in body weight and an increase in mortality. However, even at a density four times that of the natural population, mortality remained remarkably low, and this is probably a key feature allowing L. unifasciata to penetrate high up the shore. L. unifasciata feeds mainly on lichens and food levels are low over most of the zone occupied by this littorine, rising above and below this zone and being particularly high in the supralittoral immediately above the range of L. unifasciata. Thus, food cannot be a factor limiting the height that L. unifasciata extends up the shore. Experimental caging shows that the standing stock of lichen is inversely related to the density of L. unifasciata. The zonation pattern and size gradient of L. unifasciata may be due to a combination of two factors: a decline of body size due to increasing intraspecific competition at higher densities, and the tendency of L. unifasciata to migrate (probably upwards) away from areas of low food availability. The latter was experimentally demonstrated. L. unifasciata suffers from intense intraspecific competition and is responsible for limiting the availability of its food. Its populations are seemingly not regulated by predators. It borders on a zone of high food availability in which there are no important competitors. These are all circumstances favouring range expansion of the species, to the limits of physiological tolerance, to allow the species to capitalize on the adjacent rich food source.
The distribution, growth, and reproduction of the Antarctic limpet Nacella (Patinigera) concinna (Strebel, 1908)
Article
Twenty-one monthly collections of the Antarctic limpet Nacella (Patinigera) concinna (Strebel, 1908) were obtained by divers at Signy Island, South Orkney Islands. A mean monthly population density of 123.7 ± 21.2 · m−2, mean biomass of 13.7 ± 2.7 g dry tissue wt · m−2, and annual production of 2.9 g · m−2 were recorded in the depth range 2–12 m below mean low water.Shell growth was slow with a maximum growth rate, in the first 3–5 yr of life, of 3 4 mm per year. Maturity was attained at 7–8 yr (21 mm length), and maximum size (41 mm length) at about 21 yr. Unique spawning behaviour was observed in two Austral springs, and data relating spawning to the spring increase in sea temperature were obtained.
Unique spawning behaviour by the Antarctic limpet Nacella (Patinigera) concinna (Strebel, 1908)
Article
The Antarctic limpet Nacella (Patingera) concinna (Strebel, 1908) forms temporary “stacks” before spawning, a behaviour which ensures that gametes are released in close proximity. This promotes the fertilization of a large proportion of eggs, so reducing the energy outlay necessary to ensure reproductive success. The annual reproductive output of Nacella is low in comparison with other Patellidae. Rapid fertilization may also help to contain larvae in shallow coastal waters suitable for settlement. Evidence of this unique spawning behaviour has now been obtained in a series of photographs taken at Signy Island, South Orkney Islands (60°S : 43°W).