Ilmari Valovirta

Bio: Ilmari Valovirta is an academic researcher from University of Helsinki. The author has contributed to research in topics: Freshwater pearl mussel & Margaritifera. The author has an hindex of 9, co-authored 15 publications receiving 199 citations. Previous affiliations of Ilmari Valovirta include American Museum of Natural History.

Climate Warming as a Possible Trigger of Keystone Mussel Population Decline in Oligotrophic Rivers at the Continental Scale.

Abstract: The effects of climate change on oligotrophic rivers and their communities are almost unknown, albeit these ecosystems are the primary habitat of the critically endangered freshwater pearl mussel and its host fishes, salmonids. The distribution and abundance of pearl mussels have drastically decreased throughout Europe over the last century, particularly within the southern part of the range, but causes of this wide-scale extinction process are unclear. Here we estimate the effects of climate change on pearl mussels based on historical and recent samples from 50 rivers and 6 countries across Europe. We found that the shell convexity may be considered an indicator of the thermal effects on pearl mussel populations under warming climate because it reflects shifts in summer temperatures and is significantly different in viable and declining populations. Spatial and temporal modeling of the relationship between shell convexity and population status show that global climate change could have accelerated the population decline of pearl mussels over the last 100 years through rapidly decreasing suitable distribution areas. Simulation predicts future warming-induced range reduction, particularly in southern regions. These results highlight the importance of large-scale studies of keystone species, which can underscore the hidden effects of climate warming on freshwater ecosystems.

Shell morphometry, pre-mortal taphonomy and ontogeny-related growth characteristics of freshwater pearl mussel in northern Finland

Abstract: Museum collection of endangered freshwater pearl mussel (Margaritifera margaritifera) shells was studied. The ontogenetic ages of the mussels were estimated to be between 12 and 178 years. Information from shell increments, morphometry and taphonomy was combined into age-dependent life-trait reconstructions that were modelled using linear and non-linear growth functions. Nearly all the life-trait records were best explained by non-linear models and only the shell weight was best modelled by the linear growth function. In accordance with the previously set theory about the plasticity of the species life-traits and their dependence on climate and hydrogeochemistry, the shells with northern origin reached relatively large sizes with slow growth rate. The ontogenetic age could be statistically predicted using the composite dataset of life-trait information. Based on the morphometrics, we theorized that the over 60-year-old mussels are better hedged against the potential hydrological changes resulting from climat change than younger individuals.

Late Holocene climatic variability reconstructed from incremental data from pines and pearl mussels - a multi-proxy comparison of air and subsurface temperatures

Abstract: Helama, S., Laanelaid, A., Tietavainen, H., Macias Fauria, M., Kukkonen, I. T., Holopainen, J., Nielsen, J. K. & Valovirta, I. 2010: Late Holocene climatic variability reconstructed from incremental data from pines and pearl mussels – a multi-proxy comparison of air and subsurface temperatures. Boreas, Vol. 39, pp. 734–748. 10.1111/j.1502-3885.2010.00165.x. ISSN 0300-9483. Dendrochronological and sclerochronological records are mean series of arboreal and molluscan increments that are correctly aligned in time by rigorous dating. These records of tree rings and annual shell-growth increments exhibit climate signals that can be used to reconstruct fluctuations and trends in past climates. Here we present a multi-proxy reconstruction of temperature histories using a combination of dendrochronological and sclerochronological evidence. Regional curve standardization (RCS) was used to remove the non-climatic variations from dendrochronological and sclerochronological series prior to palaeoclimatic interpretation. Conventional and signal-free methods of RCS were compared. It was found that the signal-free methods produced more reliable chronologies and systematically higher climate–proxy correlations. Consequently, the temperature reconstructions were derived using the chronologies constructed by this method. Proxy-based histories of summer (July–August) temperatures were reconstructed from AD 1767 onwards. The compound use of proxies resulted in reconstructions that were of higher quality than single-proxy reconstructions. Further improvement of reconstructions was accomplished by the inclusion of lagging increment values in the transfer functions. The final multi-proxy model explained 58% of the temperature variance over the instrumental period. The multi-proxy temperature reconstruction correlated well with the long records of instrumental temperatures from Tornedalen, St. Petersburg, Uppsala and Stockholm. Overall, the reconstruction for the past 250 years agreed reasonably well with borehole temperature reconstructions obtained in northern Finland. In general, this study demonstrates the benefits of the compound use of several proxies in reconstructing climate histories. In particular, the study emphasizes the so far largely unexploited advantages of multi-proxy data sets obtained by rigorously cross-dated incremental chronologies to produce more robust palaeoclimatic reconstructions.

Polymorphism in Cepaea: A Problem with Too Many Solutions?

Abstract: When faced with a problem or a series of related problems, scientists tend to look for a single unifying solution. When alternative solutions present themselves, it is usually accepted that only one is likely to be true. Further research often justifies this assumption. The successes of this type of reasoning have tended to obscure the fact that not all biological observations must necessarily be explicable in a simple and unitary way and that not all hypotheses to be tested need be mutually exclusive. We hope to illustrate this by considering some of the evolutionary processes affecting one well known genetic polymorphism, that of shell pattern in the land snail Cepaea. rhe development of techniques for detecting molecular polymorphisms has led to considerable disagreement between those who believe that such genetic variation is actively maintained by natural selection and those who suggest that random processes are the only significant factor in its control. The most important lesson to be gained from an intensive study of the Cepaea polymorphism is that many types of evolutionary force act upon it and that their relative importance varies between different polymorphic loci, or even when the same locus is studied in different populations. It is largely meaningless to ask whether selection or drift explains the observed variation in gene frequency, or indeed to attempt to identify the single selective mechanism acting on the polymorphism. The nature of the evolutionary process means that the genetic structure of each Cepaea population usually requires a complex and perhaps a unique explanation. This is a point which has not been sufficiently emphasized by students of other polymorphic systems.

Bivalve diets in a midwestern U.S. stream: A stable isotope enrichment study

Abstract: This study examined a community of stream bivalves (unionids and fingernail clams) in a second-order woodland stream in southern Michigan using both the natural abundance of 15 N and a 6-week whole-stream 15 N enrichment experiment, as part of the Lotic Intersite Nitrogen eXperiment (LINX). Objectives included addressing what made up the diet of these bivalves and whether suspended algae consumed by bivalves were derived from pelagic phytoplankton imported from an upstream lake or attached algae sloughed from instream surfaces. Within the examination of bivalve diets, we considered whether suspension- and/or deposit-feeding modes were employed and whether bivalves selectively assimilated the algal and microbial portions of bulk material they ingested. All 12 unionid species reached a level of 15 N enrichment greater than the bulk suspended organic matter. Sphaerium striatinum (Sphaeriidae) were enriched to levels greater than all presumed food sources. Suspended algae were derived both from sloughed epilithon and pelagic phytoplankton originating from lentic waters upstream. A mixing model suggested that unionids were consuming 80% deposited and 20% suspended material. Alternatively, these bivalves were preferentially assimilating the highly enriched living component of suspended and/or benthic organic matter rather than assimilating the bulk material. These results advance our understanding of freshwater bivalve-feeding ecology, which is necessary if conservation efforts of these increasingly threatened organisms are to succeed. Freshwater bivalves were originally ubiquitous in North American rivers and streams, but they have increasingly fallen victim to anthropogenic pressures such as overharvesting, waterway impoundment, pollution, and exotic species infestation (Ricciardi and Rasmussen 1999). Bivalve conservation efforts have included translocation, but mortality rates have averaged ;50% (Cope and Waller 1995). Captive rearing programs show highly variable mussel survival rates (Dunn and Layzer 1997). Incomplete understanding of the feeding ecology of freshwater bivalves impedes successful conservation efforts. There are several ways to better understand the diet of organisms, including direct observation of feeding behavior, gut contents analysis, and examination of chemical constituents such as stable isotopes or nutrients within the tissues of organisms compared with their potential food sources. Direct observation of the feeding behavior of bivalves has

Growth and longevity in freshwater mussels: evolutionary and conservation implications

Abstract: The amount of energy allocated to growth versus other functions is a fundamental feature of an organism’s life history. Constraints on energy availability result in characteristic trade-offs among life-history traits and reflect strategies by which organisms adapt to their environments. Freshwater mussels are a diverse and imperiled component of aquatic ecosystems but little is known about their growth and longevity. Generalized depictions of freshwater mussels as ‘long-lived and slow-growing’ may give an unrealistically narrow view of life-history diversity which is incongruent with the taxonomic diversity of the group and can result in development of inappropriate conservation strategies. We investigated relationships among growth, longevity, and size in 57 species and 146 populations of freshwater mussels using original data and literature sources. In contrast to generalized depictions, longevity spanned nearly two orders of magnitude, ranging from 4 to 190 years, and the von Bertalanffy growth constant, K , spanned a similar range (0.02–1.01). Median longevity and K differed among phylogenetic groups but groups overlapped widely in these traits. Longevity, K , and size also varied among populations; in some cases, longevity and K differed between populations by a factor of two or more. Growth differed between sexes in some species and males typically reached larger sizes than females. In addition, a population of Quadrula asperata exhibited two distinctly different growth trajectories. Most individuals in this population had a low-to-moderate value of K (0.15) and intermediate longevity (27 years) but other individuals showed extremely slow growth (K = 0.05) and reached advanced ages (72 years). Overall, longevity was related negatively to the growth rate, K ,a ndK explained a high percentage of variation in longevity. By contrast, size and relative shell mass (g mm −1 shell length) explained little variation in longevity. These patterns remained when data were corrected for phylogenetic relationships among species. Path analysis supported the conclusion that K was the most important factor influencing longevity both directly and indirectly through its effect on shell mass. The great variability in age and growth among and within species shows that allocation to growth is highly plastic in freshwater mussels. The strong negative relationship between growth and longevity suggests this is an important trade-off describing widely divergent life-history strategies. Although life-history strategies may be constrained somewhat by phylogeny, plasticity in growth among populations indicates that growth characteristics cannot be generalized within a species and management and conservation efforts should be based on data specific to a population of interest.