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doi:10.1093/gerona/glq172 Advance Access published on October 21, 2010
183
BIVALVE molluscs (clams, oysters, and mussels) are
newly discovered models of natural aging (1), and the
taxonomic class includes species with the longest metazoan
life span— exceeding 400 years (2). The class Bivalvia also
holds the record within the animal kingdom for the greatest
number of species, which attain ages in excess of 150 years
(1). For example, the Geoduck clam (Panopea abrupta), the
freshwater pearl mussel (Margaritifera margaritifera), and
the ocean quahog (Arctica islandica) are all exceptionally
long lived attaining maximum ages of 163, 190, and 405
years, respectively (2–4).
In recognition of these animals attaining exceptional
ages, there has been an increasing biogerontological focus
on the group (3,5,6), and they have also been the subject of
several aging reviews (1,7,8). In addition to its use in de-
termining age, the hard calcareous shell of many bivalves
also contains an ontogenetic record of growth in the form of
annually resolved growth lines and increments (9). The
advantage of this is that bivalves sampled from a range of
environmental settings can provide reliable and accurate
information on their individual ontogenetic life history,
including their chronological age (10). Despite an increas-
ing focus on bivalves from a biogerontological perspective,
the relationship of their other life history traits to maximum
age is not as comprehensively understood as those in verte-
brate groups, such as mammals and birds. It would there-
fore be interesting to understand how life history traits and
development schedules in bivalves are related to longevity
and compare these with the relationships observed in humans
and with traditional vertebrate model aging organisms.
Factors correlating with the maximum longevity in ani-
mal groups other than molluscs have received considerable
attention, particularly with regard to life history theory
(11,12). In mammals and birds, adult body size (most com-
monly represented as body mass) correlates positively with
longevity, larger animals living, on average, longer than
smaller ones (13–16). The most plausible explanation for
the widely established relationship between body size and
longevity appears to be the role of ecological factors. For
example, larger animals are less prone to predation and thus
have lower mortality rates, which in turn leads to a greater
longevity and, according to evolutionary theory, the evo-
lution of a slower aging process (17,18). Developmental
schedules, such as time to maturity and postnatal growth
rate, have also been associated with longevity in birds and
mammals (16,19). Specifically, age at maturity is positively
correlated with maximum species longevity (20) and nega-
tively correlated with demographic aging rate (19), whereas
postnatal growth rate are negatively correlated with maxi-
mum longevity in mammals (16) and with demographic
aging rates in terrestrial vertebrates (19,21). The present
study explores whether the same relationships hold within
the Bivalvia. In the only study to investigate these life his-
tory traits in bivalves (22), concentrating on the freshwater
Maximum Shell Size, Growth Rate, and Maturation Age
Correlate With Longevity in Bivalve Molluscs
I. D. Ridgway,1 C. A. Richardson,1 and S. N. Austad2
1School of Ocean Sciences, College of Natural Sciences, Bangor University, Anglesey, United Kingdom.
2Department of Cellular and Structural Biology, Barshop Institute for Longevity and Aging Studies, University of Texas
Health Science Center San Antonio.
Address correspondence to I. D. Ridgway, PhD. Email: iain.ridgway@bangor.ac.uk
Bivalve molluscs are newly discovered models of successful aging, and this invertebrate group includes Arctica is-
landica, with the longest metazoan life span. Despite an increasing biogerontological focus on bivalves, their life history
traits in relation to maximum age are not as comprehensively understood as those in vertebrate model aging organisms.
We explore the allometric scaling of longevity and the relationship between development schedules (time to maturity and
growth rate) and longevity in the Bivalvia. Using a traditional nonphylogenetic approach and the phylogenetically inde-
pendent contrasts method, the relationship among these life history parameters is analyzed. It is demonstrated that in
bivalves, maximum shell size, development, and growth rates all associate with longevity. Our findings support the
observations of life history patterns in mammals and fish. This is the first investigation into the relationship among
longevity, size, and development schedules throughout this group, and the results strengthened by the control for phylo-
genetic independence.
Key Words: Bivalves—Longevity—Phylogenetically independent contrast analysis.
Received August 18, 2010; Accepted August 31, 2010
Decision Editor: Rafael de Cabo, PhD
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RIDGWAY ET AL.
184
that bivalve size correlates positively with maximum lon-
gevity, (b) that postmaturational longevity is proportional to
time to maturation, and (c) that the earlier a bivalve attains
its maximum asymptotic size, the shorter will be its life
span.
Materials and Methods
The symbols and abbreviations of the growth parameters
and life history traits to be investigated in this study are
listed and defined in Table 1.
Data collection: Allometric Scaling of Longevity
Initially, we set out to investigate the relationship
between body mass and maximum life span (Tmax) in
bivalves in a similar manner to that which has been carried
out by de Magalhães and colleagues (16) for a range of
other animal groups. Unfortunately, body mass and maxi-
mum age data are unavailable for molluscs in sufficient
quantities to allow meaningful analyses to be undertaken.
However, data were available on maximum bivalve size,
that is, the maximum asymptotic size (L∞; shell length or
shell height) derived from the Von Bertalanffy growth
equation (31,32). We have therefore used this dimension
rather than mass in our analyses.
The values for Tmax that we have used refer to the pub-
lished reported maximum life span of the oldest animal re-
corded in a population or the longevity estimate obtained
from an age frequency analysis. Many species of bivalves
contain a growth record in the form of annually deposited
internal shell increments, and therefore, estimates of the age
of individual bivalves are accurate and reliable (9). Using
these two parameters (L∞ and Tmax), the allometric relation-
ship between body size and longevity was investigated. To
what extent Tmax is an accurate estimation of the rate of ag-
ing depends critically on the number of individuals sampled
in a population, and the rate of mortality increase with age,
so its utility has been a source of debate (15,16). The con-
sensus is that to the extent that it measures real differences
in achieved longevity, differences in Tmax are proportional
to genetic limitations on longevity among species. Thus, it
has been argued to be related to a species’ rate of physiolog-
ical aging (33–35). There are additional estimates of aging
rate, which could be used in place or alongside Tmax, such as
the mean adult longevity or adult mortality rate doubling
time, which is a demographic measurement of aging. How-
ever, the greater availability of estimates of Tmax in the liter-
ature governed our decision to use this parameter as the
estimator of aging rate.
Data Collection: Developmental Schedules and Longevity
In the second part of our study, we investigated the rela-
tionship between developmental rate and longevity. Any
estimate of species longevity incorporates developmental
Table 1. Symbols and Abbreviations Used in This Study
Parameter Definitions
KParameter of the von Bertalanffy growth function, of dimension
per year, expressing the rate at which the asymptotic length is
approached
L∞Asymptotic length in millimeters; parameter of the VBGF
expressing the mean length that the species would reach if
indefinite growth
Tsex Age at first maturity (years)
Tmax Maximum age or life span reached in a population (years)
Tad Age at first maturity substituted from the maximum age
(Tmax − Tsex)
VBGF von Bertalanffy growth function, used to describe the growth in
length of fish and marine invertebrates
mussels, concluded that overall, longevity was negatively
related to the growth rate, which explained a high percentage
of variation in longevity. By contrast, size and relative shell
mass explained little variation in longevity.
Through the application of the phylogenetically inde-
pendent contrast (PIC) method of Felsenstein (23), which
statistically removes bias due to the effects of shared evolu-
tionary history, de Magalhães and colleagues (16) demon-
strated that time to maturity is associated with adult life
span in mammals, with evidence suggesting an even stronger
association than previously thought. The length of time a
mammal will live after maturity, that is, its adult life span, is
proportional to the amount of time it took to reach maturity.
Ricklefs (19) noted the same relationship between time to
maturity and actuarial aging more generally across all
terrestrial vertebrates.
We investigate the allometric scaling of longevity and
whether there is a relationship between development schedules
and longevity in bivalves. Using a traditional nonphyloge-
netic approach (ie, simple regression of species values at the
tip of the phylogeny), the relationship between maximum
asymptotic size and maximum longevity was initially ana-
lyzed (see Table 1). Although traditional nonphylogenetic
approaches have been historically used in comparative
biology; it has been clearly demonstrated during the last 20
years that interspecific comparisons can be potentially
compromised by statistical nonindependence of species
values (23–26), leading to unacceptably high Type I error
rates (incorrectly accepting alternate hypotheses) and
inaccurate estimations of correlations or slopes (27–29),
although under what circumstances such concerns are war-
ranted is not clear (30).
The overall aim of our study is to investigate whether
bivalves demonstrate similar life history strategies to those
of terrestrial vertebrates where body size and developmen-
tal schedules are associated with longevity and therefore
possibly with aging rates. In addition, species that do not fit
the allometry of life span may hold clues about the evo-
lutionary forces shaping longevity and aging (16). In this
article, we specifically investigate using previously pub-
lished data three hypotheses related to bivalve longevity (a)
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CORRELATES OF LONGEVITY IN BIVALVES 185
time, that is, time from birth to maturation, potentially
adding bias to the analysis as discussed by de Magalhães
and colleagues (16). Therefore, for this analysis, we have
used the maximum adult life span (Tad), which is defined
as Tmax minus age at sexual maturity (Tsex). Bivalves
have varying reproductive strategies, including brooding,
for example, some oyster species, although the majority
employ external fertilization; therefore, Ts ex can be de-
fined simply as the age at which reproductive maturity is
attained. Using these two parameters (Tad and Tsex), the
relationship between development rate and longevity was
investigated.
For proxy measures of developmental schedules, Tsex
was used as a measure of a bivalve’s growth rate. Previous
investigations of terrestrial vertebrates have used postnatal
growth rate as a measure of developmental schedule (16,19);
however, such data are unavailable for bivalves. Instead, we
used the van Bertalanffy growth coefficient K (per year), an
appropriate alternative that is widely available in the litera-
ture. This parameter expresses the rate at which L∞ is
approached. Tsex is later demonstrated (see results later) to
be directly proportional to adult life span. Therefore, the
relationship between K and total longevity is investigated,
not simply adult life span, due to the nature of available
data.
We obtained from the literature growth and life history
parameters for a total of 111 species and populations of
bivalves from natural marine or estuarine or freshwater en-
vironments. The phylogenetic range of the bivalves in-
cluded in each of the regression analyses and the PIC s are
presented in Table 2. In instances where the literature pro-
vided estimates for both sexes of a species, the arithmetic
mean of the two was used. To exclude potentially problem-
atic growth parameter estimates, data from species sampled
from within heavily fished or other anthropogenically im-
pacted areas were not included in our analyses. It is reason-
ably assumed that in such areas, estimates of Tmax are not
reliable or representative of the actual achievable longevity
for that species.
Table 2. The Phylogenetic Coverage of the Bivalves Included in the
Regression Analyses and the Analyses of Phylogenetic Independent
Contrasts
Parameters N
No. of
Species
No. of
Families
No. of
Orders
No. of
Bivalve
Subclasses
%
Heterodonta
L∞ vs. Tmax 56 56 25 7 4 70
Tad vs. Tsex 50 50 20 6 3 70
Tmax vs. K35 35 20 6 4 82
Contrasts
Contrasts of
L∞ vs. Tmax
55 56 25 7 4 n/a
Contrasts of
Tad vs. Tsex
49 49 20 6 3 n/a
Contrasts of
Tmax vs. K
34 35 20 6 4 n/a
Statistical Analyses
A traditional nonphylogenetic approach (ie, simple
regression of species values ignoring phylogeny) was initially
used to compare the relationship between five different
parameters (L∞, Tmax, Tad, Tsex, and K). To meet the assump-
tions required for least squares linear regression, data were
ln-transformed prior to statistical analysis. Although tradi-
tional nonphylogenetic approaches have been widely used
in comparative biology, computer simulations (27,28) have
demonstrated that such approaches can lead to unaccept-
ably high Type I error rates (incorrectly accepting alternate
hypotheses) and inaccurate estimations of correlations or
slopes (29). To assess these potential problems, significant
correlations from the traditional analyses were further
investigated using the PIC method of Felsenstein (23).
Standardized independent contrasts were computed fol-
lowing the methods of Garland and Janis (29) and Garland
and Adolph (36). To assure contrasts were appropriately
standardized, the absolute values of the standardized con-
trasts were correlated with their standard deviations; if no
correlation was apparent, the branch lengths adequately
standardized the independent contrasts as described (37).
The relationship between the standardized independent
contrasts is investigated through ordinary least squares re-
gression analysis, with regression lines constrained to pass
through the origin (24,27,37–39). During the statistical
analysis of PIC s, associated p values can generally be
determined by reference to conventional statistical tables
(36). Therefore, the significance level was set at .05.
Phylogenetic Information
Although the precise topological structure of the bivalve
phylogenetic tree is not completely resolved, the general re-
lationships between the taxa are (for bivalve phylogenies,
see (40–45)). This enabled a phylogenetic tree to be created
(Figure 1), which contained accurate relationships of all the
species used in the study. Where possible, the branch length
data from Taylor and colleagues (45) were used; where no
branch length data were available, an arbitrary branch
length was used, this length was the mean of all branch
lengths contained in the Taylor and colleagues (45) phylog-
eny, with branch lengths in the units substitutions per site.
Although this latest molecular phylogeny was largely
constructed to describe the phylogeny of the Heterodonta,
Taylor and colleagues (45) utilized species from the
order Palaeoheterodonta (Trigoniidae, Margaritiferidae,
and Unionidae) as outgroups, so there is broad coverage of
the class Bivalvia.
Provided accurate phylogenetic topologies and branch
lengths are used, the statistical power of independent con-
trasts is identical to that of traditional nonphylogenetic
approaches (36). Although it is not ideal to utilize arbitrary
branch lengths, computer simulations have demonstrated
that independent contrasts are reasonably robust with
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RIDGWAY ET AL.
186
to adult life span, explaining 48.4% and 30.2% of the
variation, respectively. These results strongly suggest that
development time, measured as time to maturity, not only
influences adult life span but also may coevolve with adult
life span. The amount of time a bivalve will live after matu-
rity, that is, its adult life span, is proportional to the amount
of time it took to attain maturity.
Growth Rate and Longevity
We then investigated the relationship between growth
rate (K per year) and longevity (Figure 4). Analysis of 50
species demonstrated a robust significant negative relation-
ship between K and Tmax using either nonphylogenetic
(Figure 4) or PIC analyses (Table 3), explaining 64.3% and
61.9% of the variance, respectively. These results indicate
that the faster a bivalve grows, the shorter its life span.
Discussion
This study is the first to investigate in invertebrates the
much documented relationships between longevity and size
and development schedules that occur in terrestrial verte-
brates (16,19). More importantly, it investigates these rela-
tionships in the exceptionally long-lived molluscan class
Bivalvia.
respect to violation of assumptions (including errors in
branch lengths: (28,46,47) providing arbitrary branch lengths
are appropriately checked for statistical adequacy (37)).
Results
Allometric Scaling of Longevity With Size
Data from 56 species of bivalves reveal a statistically sig-
nificant positive impact of L∞ on Tmax (Figure 2, Table 2),
although only 13.1% of the variation in maximum longevity
is accounted for by asymptotic size. PIC analysis of the
same 56 species confirmed this relation and even enhanced
the statistical significance (Table 3). This result suggests
that the evolution of body size in bivalves is associated with
that of longevity.
Developmental Schedules and Longevity
Data from 35 bivalve species were used to investigate the
relationship between adult life span and age at maturity (in
years; Table 2). In both traditional (Figure 3) and PIC analy-
sis (Table 3), age at sexual maturity was significantly related
Table 3. Results of the Regression Analysis for Each Set of
ln-Transformed Data, Documenting the df, r2 Value, F Statistic,
and Associated p Value
Parameters df r2F statistic Associated p Value
L∞ vs. Tmax 56 .131 8.721 .004*
PIC L∞ vs. Tmax 55 .138 11.278 .001*
Tad vs. Tsex 50 .484 30.912 <.001*
PIC Tad vs. Tsex 49 .302 18.995 <.001*
Tmax vs. K35 .643 86.343 <.001*
PIC Tmax vs. K34 .619 80.718 <.001*
* Indicates the result is statistically significant at the 95% level. PICs =
phylogenetically independent contrasts.
Figure 2. The relationship between the natural log of the asymptotic length
(L∞; centimeters), derived from the von Bertalanffy growth formula, and the
natural log of the maximum age (Tmax; years) attained by bivalve species. Non-
phylogenetic regression analysis: n = 56, F = 8.72 and p = .004, r2 = .137.
Figure 1. Phylogenetic relationships of the class Bivalvia documenting the relationships between the four main subclasses and the main speciose orders and
superfamilies (drawn from (45)).
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CORRELATES OF LONGEVITY IN BIVALVES 187
Allometric Scaling of Body Size and Longevity
In multiple vertebrate taxa, there is a well-established
relationship between body size and longevity (16,48), for
which de Magalhães and colleagues (16) suggest that evolu-
tionary ecological factors appear the most plausible expla-
nation. Simply, larger species are believed to be less prone
to predation and therefore experience lower mortality rates,
as seen in fish by Pauly (49). Greater survivorship in turn
leads to longer life spans and, according to evolutionary
theory, the evolution of a slower aging process (17,18).
We have demonstrated that body size in bivalves signifi-
cantly correlates with longevity, a relationship that has been
observed in many other animal taxonomic groups, includ-
ing mammals (16) and freshwater mussels (22). Although a
significant relationship was observed, body size in bivalves
explains far less of the variation in longevity than in other
taxonomic groups, only 13% compared with 49% in birds
(16) and 66% in mammals (16). The mammalian data are
probably the least analogous comparison deriving from
largely captive populations. This reduced relationship
between longevity and size in bivalves may be due to con-
founding factors such as burrowing ability and shell
thickness among the group, factors that strongly influence
their vulnerability to predation. For example, Kirby (50)
demonstrated that in two species of the oyster genus,
Crassostrea, longevity is strongly influenced by shell thick-
ness, suggesting that shell thickness may provide greater
resistance to extrinsic hazards (eg, predation or fluctuations
in temperature) leading to a longer life.
Recent analyses investigated the relationship between
size and longevity in the fresh water mussels and obtained
similar results, although a significant positive correlation
between size and longevity, size, and relative shell mass
explained little variation in longevity (22).
Developmental Schedules and Longevity
Evolutionary theories of aging propose that the rate of
aging is caused by the force of natural selection acting to
optimize fitness early in life (51). The antagonistic pleiot-
ropy theory of aging suggests the existence of pleiotropic
genes that endow benefits early in life at the cost of delete-
rious effects later to explain the evolution of senescence
(52), therefore proposing a trade-off between reproduction
and longevity. In a classic article, Williams (52) expounded
that reproductive maturation is the most significant mile-
stone in the evolution of senescence and that senescence
may theoretically initiate immediately after this stage in
development, that is, “the sooner this point is reached,
the sooner senescence should begin and the sooner it
should have demonstrable effects.” Therefore, according
to the theory, the time a bivalve will live after maturity
should be proportional to the amount of time it took to
reach maturity.
Mammalian maximum adult life span correlates with age
at maturity (16,20). In support of these findings, Ricklefs
(19) demonstrated that age at maturity is negatively corre-
lated with demographic aging rate in terrestrial vertebrates.
Ricklefs (19) states that the rate of aging within a species is
primarily related to that of extrinsic mortality, and those
young individuals must wait longer to enter the breeding
population in species with lower extrinsic mortality rates.
We have shown that maximum adult life span in bivalves
is also significantly and positively correlated with age at
maturity, a correlation that is predicted by the antagonistic
pleiotropy theory of aging.
It has been suggested that the optimization theories of
aging, including the antagonistic pleiotropy and the dispos-
able soma theories of aging, may not be relevant to animals
that demonstrate neither a decrease in fecundity with age or
an observable decline in their fitness (53). In longer lived
bivalves, there is no evidence of reproductive senility and
gonad production continues, regardless of age, and as there
is indeterminate growth (although a minimal amount at ad-
vanced ages), gonad production is reported to actually in-
crease with age (54,55). Although at the individual level this
will be the case, it is almost inconceivable that the mortality
rate (age dependant and age independent) would not result
Figure 3. The relationship between the natural log of the age at sexual
maturity (Tsex) and the natural log of the adult life span (Tad; years) attained by
bivalve species. Nonphylogenetic regression analysis: n = 50, F = 30.912 and
p ≤ .001, r2 = .484.
Figure 4. The relationship between the natural log of the maximum age
(years) attained by bivalve species (Tmax) and the natural log of the growth
coefficient K as derived from the von Bertalanffy growth formula for bivalve
species. Nonphylogenetic regression analysis: n = 35, F = 86.343 and p ≤ .001,
r2 = .643.
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RIDGWAY ET AL.
188
in the older cohort of clams leaving less gametes than the
younger cohorts (increase in gamete production with age in
the population would be offset by loss of individuals from
the population), which, according to the two optimization
theories of aging, would result in natural selection acting to
optimize fitness early in life, that is, senescence will creep
into a population, albeit at a slow rate. These longer lived
bivalves have also been suggested to be good examples of a
group of organisms displaying negligible senescence (56)
or possibly negative senescence (57). Our findings here
align with, and were predicted by, the antagonistic theory of
aging. Regardless of the growth and reproductive character-
istics of the taxonomic class, we suggest that antagonistic
pleiotropy is still a relevant theory for explaining aging in
bivalves because, at the population level, the rate of extrin-
sic mortality results in a decrease in gamete production per
age cohort, despite gamete production increasing with
age at the individual level (55) and hence a reduction in
the strength of natural selection with age.
The final hypothesis investigated the relationship
between shell growth rate, another proxy measure of the
developmental schedule, and longevity. Longevity is
significantly negatively correlated with growth rate, ex-
pressed as the von Bertalanffy growth coefficient (K). In
mammalian species, de Magalhães and colleagues (16)
demonstrated that a fast postnatal growth rate in mam-
mals is associated with a shorter life span. Furthermore,
Ricklefs and Scheuerlein (21) and Ricklefs (19) have
demonstrated that postnatal growth rate is negatively
correlated with demographic aging rates in terrestrial
vertebrates. Although the von Bertalanffy growth coeffi-
cient (K) is not the precise equivalent of postnatal growth
rate, it is the closest analogous parameter available for
bivalves. In the freshwater mussels, Haag and Rypel (22)
also demonstrated longevity related negatively to the
growth rate, K, which explained more than 75% of varia-
tion in longevity. These patterns remained when data
were corrected for phylogenetic relationships among
species, and furthermore, path analysis supported the
conclusion that K was the most important factor influ-
encing longevity both directly and indirectly through its ef-
fect on shell mass (22).
The two most commonly accepted optimization theories
of aging, the antagonistic pleiotropy and the disposable
soma theories of aging, suggest that growth rate should be
associated with the life span of a species. Kirkwood and
Holliday (58), the proponents of the disposable soma theory
of aging, argue that “it may be selectively advantageous for
higher organisms to adopt an energy-saving strategy of re-
duced accuracy in somatic cells to accelerate develop-
ment and reproduction, but the consequence will be
eventual deterioration and death.” Therefore, longevity is
determined through the trade-offs between resources spent
on somatic maintenance and reproduction (59). Williams
(52) similarly predicted a trade-off between reproduction
(reproductive success, fitness, and vigor) and longevity as
part of the antagonistic pleiotropy model stating that “rapid
individual development should be correlated with rapid
senescence.”
Growth rate had much greater explanatory power (in
terms of the r2 value) than either age at maturity or shell
size. The explanatory power of growth rate on longevity
observed in bivalves was very similar to that in other taxo-
nomic groups, 0.67 in both mammals (not including ceta-
ceans) and birds (16). Haag and Rypel (22) found similar,
stating that 75% of the variation in the longevity of fresh-
water mussels was explained by the growth rate. It is prob-
able that the reduced accuracy in somatic maintenance
associated with the rapid growth rate has the most direct
influence longevity, whereas the other parameters hold a
more indirect complex relationship or there maybe con-
founding factors. As mentioned previously, the reduced re-
lationship between longevity and size in bivalves may be
due to confounding factors, which strongly influence their
vulnerability to predation and other extrinsic factors (eg,
burrowing and shell thickness).
Conclusions
This is the first demonstration of a relationship between
longevity, size, and development schedules in bivalves,
newly discovered models of natural aging (1), and the
results are strengthened by the control for phylogenetic
independence. From our results, it appears that in
bivalves, maximum size, development, and growth are as-
sociated with longevity, and these findings are in accord
with the two main evolutionary theories of aging and sup-
port the findings of other researchers working on mam-
mals and fish. However, in comparison with the
vertebrate studies to date, there is a reduced relationship
between longevity and size in bivalves. These results
therefore have implications in the design and interpretation
of comparative studies of aging in bivalves. When investi-
gating similar relationships in mammals, de Magalhães
and colleagues (16) concluded that “developmental sched-
ules such as the time to maturity and growth rates have a
physiological basis that should be taken into consideration
in the comparative biology of aging.” Ignoring this re-
quirement may result in incorrectly assuming that the
mechanisms involved in development are associated
with aging rather than as a consequence of the correlation
between developmental schedules and longevity (16,60).
To further understand the actual biologic mechanisms that
cause species to display different rates of aging, more de-
tailed biochemical and molecular investigations are re-
quired (16).
Funding
This work was supported by a National Institute on Aging/Biotechnology
and Biological Sciences Research Council Partnering Award to Support
Collaborative Research on the Biology of Aging (R01).
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CORRELATES OF LONGEVITY IN BIVALVES 189
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