Mitochondrial Plasticity in Brachiopod (Liothyrella Spp.) Smooth Adductor Muscle As a Result of Season and Latitude
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Mar Biol (2010) 157:907–913 DOI 10.1007/s00227-009-1374-z ORIGINAL PAPER Mitochondrial plasticity in brachiopod (Liothyrella spp.) smooth adductor muscle as a result of season and latitude Glenn J. Lurman • Till Blaser • Miles Lamare • Lloyd S. Peck • Simon Morley Received: 17 September 2009 / Accepted: 9 December 2009 / Published online: 24 December 2009 Ó Springer-Verlag 2009 Abstract Habitat temperature and mitochondrial volume was unchanged, and Sv(im,mt) was significantly increased. density (Vv(mt,mf)) are negatively correlated in fishes, while Thus, seasonal acclimatization to the cold resulted in the seasonal acclimatization may increase Vv(mt,mf) or the same number of more reactive mitochondria. L. neozela- surface density of the mitochondrial cristae (Sv(im,mt)). The nica was clearly able to adapt to seasonal changes using a effect of temperature on invertebrate mitochondria is different mechanism, i.e. primarily through regulation of essentially unknown. A comparison of two articulate bra- cristae surface area as opposed to mitochondrial volume chiopod species, Liothyrella uva collected from Rothera density. Furthermore, given the evolutionary age of these Station, Antarctica in summer 2007, and Liothyrella living fossils (i.e. approximately 550 million years), this neozelanica collected from Fiordland, New Zealand in suggests that mitochondrial plasticity has roots extending winter 2007 and summer 2008, revealed a higher Vv(mt,mf) far back into evolutionary history. in the Antarctic brachiopod. The Sv(im,mt) was, however, significantly lower, indicating the Antarctic brachiopods have more, less reactive mitochondria. L. uva, from the Introduction colder environment, had larger adductor muscles in both absolute and relative terms than the temperate L. neozela- Temperature has significant effects on the physiology of nica. Furthermore, a seasonal comparison (winter vs. ectotherms and is often seen as a master regulator affecting summer) in L. neozelanica showed that the absolute and the whole animal on a number of levels including muscle relative size of the adductor increased in winter, Vv(mt,mf) function. Muscle is a highly plastic tissue and a host of compensatory mechanisms on a number of levels ranging from molecular through to organelles are employed to Communicated by J. P. Grassle. maintain function (Egginton and Sidell 1989; Johnston Electronic supplementary material The online version of this 1993;Sa¨nger 1993; Watabe 2002). In fish, mitochondria article (doi:10.1007/s00227-009-1374-z) contains supplementary are subject to reductions in efficiency as temperature material, which is available to authorized users. decreases because increased unsaturated fatty acids are needed to maintain mitochondrial membrane fluidity at low G. J. Lurman Á L. S. Peck Á S. Morley British Antarctic Survey, Madingley Road, temperatures (Logue et al. 2000; Guderley 2004b), which High Cross, Cambridge CB3 0ET, UK leads to increased proton leak across the membrane (Brand et al. 1991; Guderley 2004a). The thermodynamic effects Present Address: of reduced temperature also lead to a reduction in enzyme G. J. Lurman (&) Á T. Blaser Institute for Anatomy, University of Bern, activity (Sa¨nger 1993; Guderley 2004b). Compensatory Baltzerstr. 2, 3000 Bern 9, Switzerland mechanisms include improved catalytic efficiency by the e-mail: [email protected] expression of different enzyme isoforms (Crockett and Sidell 1990; Guderley 2004b), increasing the mitochondrial M. Lamare Portobello Marine Lab, University of Otago, volume density (Sa¨nger 1993; Johnston et al. 1998) and in Dunedin, New Zealand one study, the mitochondrial cristae surface density, i.e. the 123 908 Mar Biol (2010) 157:907–913 ‘‘amount’’ of cristae packed within a mitochondrion also surface (Cornelisen and Goodwin 2008). The Antarctic increased in the cold (St-Pierre et al. 1998). L. uva near Rothera, on the other hand, experiences very Although this is well characterised in fish, it is largely stable but extremely cold seawater temperatures of -1.8 to unknown whether the effects and mechanisms are the same ?1.0°C. in invertebrates. At best, only a handful of studies have examined the effects of temperature on mitochondrial plasticity in invertebrates. One laboratory study measured Methods mitochondrial density in different populations of the same polychaete (Arenicola marina) from different latitudes, i.e. Specimen collection the North Sea and the White Sea, in response to thermal acclimation. A 2.4-fold increase was found in the mito- Antarctic L. uva (Fig. 1) were collected by SCUBA diving chondrial volume density in the White Sea A. marina near Rothera Station, Adelaide Island (67°34.250S, compared to the North Sea specimens (Sommer and Po¨rt- 68°08.000W) from 20 m depth in February 2007 (N = 8). ner 2002). The cristae surface density was not measured in Brachiopods were transported back to the UK where they their study and is seldom measured in the majority of were held for 3 months in a re-circulating seawater studies concerning temperature. Therefore, the possibility aquarium maintained at 0°C and a 16-h light/8-h dark that polychaetes also increase the cristae surface density in photoperiod. Biological filtration and regular water chan- their mitochondria in the cold cannot be excluded. ges maintained seawater quality. Brachiopods were feed an More recent work has investigated mitochondrial vol- algal suspension (Nannochloropsis sp., Instant AlgaeÒ). ume density in the Antarctic limpet Nacella concinna from Temperate L. neozelanica (Fig. 1) were collected by different latitudes in the Southern Ocean (Morley et al. SCUBA divers also from approximately 20–30 m depth in 2009). There was evidence of mitochondrial plasticity in Doubtful Sound, New Zealand (167°02.910E, 45°20.920S). the foot muscle. However, there was no evidence for the Collections were made both in winter (July 2007, N = 8) expected change in mitochondrial volume density and the when the seawater temperature was 11°C and in summer key response reported was through a change in mitochon- (February 2008, N = 8) when the water temperature was drial cristae surface area (Morley et al. 2009). While the 17°C. The L. neozelanica were kept in a bucket of seawater results of this study are interesting, in particular, because for a maximum of 2 h before they were prepared for tissue they demonstrated that even stenothermal Antarctic fixation on shore at the University of Otago’s Deep Cove invertebrates can exhibit a certain degree of mitochondrial field station in Doubtful Sound. plasticity, they are limited precisely because they come from a stenothermal invertebrate (although it can be argued Brachiopod tissue preparation that being intertidal, N. concinna is one of the more eurythermal Antarctic invertebrates). Shell length was measured (±0.01 mm) with vernier To determine whether the paradigm of mitochondrial callipers, and wet weight (±0.01 g) was determined both plasticity in response to temperature change is applicable to when the mantle was full of seawater and when empty. an even broader group of invertebrates, a completely dif- The anterior portions of both valves were cut away with ferent animal phylum was selected, the Brachiopoda. Fur- scissors exposing the mantle cavity but leaving the thermore, the present study provided the opportunity to majority of the two valves, the hinge and consequently investigate whether these invertebrates are capable of the muscles intact and attached to both valves. This adaptation on both evolutionary and/or seasonal scales. allowed in situ fixation of all muscles at their normal This was possible because two species from the same contracted length. Brachiopods were fixed for 24 h in 3% genus, Liothyrella uva from the Antarctic Peninsula and glutaraldehyde containing 0.05 M PIPES pH 7.6, 0.3 mM Liothyrella neozelanica from Fiordland, New Zealand were calcium chloride, 7 mM sucrose and 0.77 mM sodium studied. Articulate brachiopods such as Liothyrella spp. are azide. The osmolality was similar to that of seawater filter feeders predominantly living off phytoplankton (800 mOsm kg-1). After primary fixation, the brachio- (Rhodes and Thayer 1991; Peck et al. 2005). They are pods were washed three times with, and stored for traditionally described as common in polar regions, the 5 weeks in the same solution as earlier, without the glu- deep sea and fiordic environments (James et al. 1992). In taraldehyde and sodium azide. Fiordland, New Zealand, they occur at depths of 15–50 m. Smooth adductor muscles were dissected free from their L. neozelanica experiences a broad range of temperatures attachment points and care was taken not to destroy the in Fiordland, where winter temperatures may be as low as natural form. Muscles were dried with tissue paper and 9°C and summer maxima 18°C, although this varies with weighed (±2 mg) and then weighed again in fixative to depth, and there is even greater variation close to the determine the tissue density (1.018). Care was again taken 123 Mar Biol (2010) 157:907–913 909 whole adductor muscle was sectioned transversely at approximately half the length of the adductor muscle using a Reichert ultramicrotome. Sections were stained with methylene blue. Ultrathin sections (80 nm) were placed on copper grids (200 mesh). Grids were then stained for 5 min in uranyl acetate saturated 50% methanol and then for 5 min in lead citrate. Morphometry Methylene blue stained semi-thin sections were analysed using a Zeiss Axioskop at 1009 magnification fitted with an Olympus DP70 digital camera that was connected to a computer. Frames were selected randomly by starting in the top left corner and sampling every 5th frame with ten frames sampled, i.e. 250 myocytes. The maximum cell diameter (lm) was determined to be the distance between the two most distant myocyte edges perpendicular to the longitudinal axis of the cell and was measured using the arbitrary distance function in the Olympus DP software, version 3.2. The relative mitochondrial volume density (Vv(mt,mf)), given as a proportion of muscle fibre volume, was deter- mined as per Morley et al.