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Peripheral populations occupy the edge of a species' range and may exhibit adaptations to potentially “harsher” marginal environments compared with core populations. The peripheral population of Spotted Gar Lepisosteus oculatus in the Great Lakes basin represents the northern edge of the species' range and is completely disjunct from the core Mississippi River basin population. Age-0 Spotted Gars from the peripheral population experience a growing season approximately half that of the core population but reach similar sizes by winter, suggesting potential for countergradient variation in growth, i.e. an evolutionary response to an environmental gradient such as latitude to compensate for the usual phenotypic effect of that gradient. In this study we used two common garden experiments to investigate potential countergradient variation in growth of young-of-year Spotted Gars from peripheral populations in comparison with those from core populations. Our first experiment showed that in a common environment under temperatures within the first growing season (22–24°C), Spotted Gars from the peripheral population had significantly higher growth rates than those from the core population. Final Spotted Gar weight–length ratio was also higher in the peripheral versus core population. In our second experiment, under three temperature treatments (16, 23, and 30°C), maximum growth occurred at the highest temperature, whereas growth ceased at the lowest temperature for both populations. These results suggest that important genetic and physiological differences could exist between the two population groups, consistent with countergradient variation. Our findings indicate that countergradient growth variation can occur even in relatively slowly evolving fishes, such as gars (family Lepisosteidae), and that protection of peripheral populations should be a key component of fish conservation planning.
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Evidence of Countergradient Variation in Growth of
Spotted Gars from Core and Peripheral Populations
Solomon R. Davida, Richard S. Kik IVb, James S. Dianac, Edward S. Rutherfordd & Michael J.
Wileyc
a Daniel P. Haerther Center for Conservation and Research, John G. Shedd Aquarium, 1200
South Lake Shore Drive, Chicago, Illinois 60605, USA
b Belle Isle Conservancy, 8109 East Jefferson, Detroit, Michigan 48214, USA
c School of Natural Resources and Environment, University of Michigan, 440 Church Street,
Ann Arbor, Michigan 48109-1041, USA
d National Oceanic and Atmospheric Administration, Great Lakes Environmental Research
Laboratory, 4840 South State Road, Ann Arbor, Michigan 48108-9719, USA
Published online: 29 Jun 2015.
To cite this article: Solomon R. David, Richard S. Kik IV, James S. Diana, Edward S. Rutherford & Michael J. Wiley (2015)
Evidence of Countergradient Variation in Growth of Spotted Gars from Core and Peripheral Populations, Transactions of the
American Fisheries Society, 144:4, 837-850, DOI: 10.1080/00028487.2015.1040523
To link to this article: http://dx.doi.org/10.1080/00028487.2015.1040523
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ARTICLE
Evidence of Countergradient Variation in Growth of
Spotted Gars from Core and Peripheral Populations
Solomon R. David*
Daniel P. Haerther Center for Conservation and Research, John G. Shedd Aquarium,
1200 South Lake Shore Drive, Chicago, Illinois 60605, USA
Richard S. Kik IV
Belle Isle Conservancy, 8109 East Jefferson, Detroit, Michigan 48214, USA
James S. Diana
School of Natural Resources and Environment, University of Michigan, 440 Church Street, Ann Arbor,
Michigan 48109-1041, USA
Edward S. Rutherford
National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Laboratory,
4840 South State Road, Ann Arbor, Michigan 48108-9719, USA
Michael J. Wiley
School of Natural Resources and Environment, University of Michigan, 440 Church Street, Ann Arbor,
Michigan 48109-1041, USA
Abstract
Peripheral populations occupy the edge of a species’ range and may exhibit adaptations to potentially “harsher”
marginal environments compared with core populations. The peripheral population of Spotted Gar Lepisosteus
oculatus in the Great Lakes basin represents the northern edge of the species’ range and is completely disjunct from
the core Mississippi River basin population. Age-0 Spotted Gars from the peripheral population experience a
growing season approximately half that of the core population but reach similar sizes by winter, suggesting
potential for countergradient variation in growth, i.e. an evolutionary response to an environmental gradient such
as latitude to compensate for the usual phenotypic effect of that gradient. In this study we used two common garden
experiments to investigate potential countergradient variation in growth of young-of-year Spotted Gars from
peripheral populations in comparison with those from core populations. Our first experiment showed that in a
common environment under temperatures within the first growing season (22–24C), Spotted Gars from the
peripheral population had significantly higher growth rates than those from the core population. Final Spotted Gar
weight–length ratio was also higher in the peripheral versus core population. In our second experiment, under three
temperature treatments (16, 23, and 30C), maximum growth occurred at the highest temperature, whereas growth
ceased at the lowest temperature for both populations. These results suggest that important genetic and
physiological differences could exist between the two population groups, consistent with countergradient variation.
Our findings indicate that countergradient growth variation can occur even in relatively slowly evolving fishes, such
as gars (family Lepisosteidae), and that protection of peripheral populations should be a key component of fish
conservation planning.
*Corresponding author: sdavid@sheddaquarium.org
Received December 14, 2014; accepted April 6, 2015
837
Transactions of the American Fisheries Society 144:837–850, 2015
ÓAmerican Fisheries Society 2015
ISSN: 0002-8487 print / 1548-8659 online
DOI: 10.1080/00028487.2015.1040523
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The loss of biodiversity is a global crisis threatening all
major habitats and ecological scales (United Nations 1992).
The loss of local species populations can have cascading
effects, influencing entire ecosystems and disrupting important
ecosystem services (Garner et al. 2005; Hooper et al. 2005;
Helfman 2007). Furthermore, the relationship between species
and ecosystem services is mainly a function of the size of local
populations, not just the overall existence of species them-
selves (Luck et al. 2003). Therefore, conserving distinct local
populations (population diversity; Luck et al. 2003) is an
essential part of the conservation of biodiversity.
Peripheral or “fringe” populations occupy the edge of a spe-
cies’ range and are considered to be exceptionally important in
terms of a species’ ecology, biogeography, evolution, and con-
servation (Scudder 1989; Lesica and Allendorf 1995; Latta
2003). Peripheral populations often persist under environmen-
tal conditions distinct from those experienced by the species’
central or “core” populations and therefore may exhibit spe-
cific genetic and phenotypic adaptations to potentially
“harsher” environments (Yakimowski and Eckert 2007). Due
to small size, fragmentation, or complete disjunction, many
peripheral populations have low recolonization potential and
therefore are more susceptible to environmental perturbations,
as well as extinction (Lesica and Allendorf 1995; Channell
and Lomolino 2000; Wisely et al. 2004). Peripheral popula-
tions also often experience very low gene flow and high
degrees of genetic drift, leading to further divergence from
core populations (Jones et al. 2001; Lammi et al. 2001; Johan-
nesson and Andre 2006).
Because of differing environmental conditions related to
geographical factors such as latitude, populations may also
exhibit different reaction norms, which in turn affect various
life history characteristics, such as size and age at maturity,
growth rate, or fecundity (Stearns and Koella 1986; Berrigan
and Koella 1994; Power and McKinley 1997; Munch et al.
2003; Heibo et al. 2005; Slaughter et al. 2008). Such latitudi-
nal variation in life history characteristics has been observed
in many different taxa including plants (Yakimowski and Eck-
ert 2007), mammals (Kyle and Strobeck 2002), reptiles (Wil-
son and Cooke 2004), invertebrates (Lee et al. 1998; Lardies
et al. 2004), and fish (Kynard 1997; Yamahira and Conover
2002; Foster and Vincent 2004). Coupled with genetic drift
and low gene flow, these latitudinal variations in life history
characteristics may contribute to evolutionary divergence
between peripheral and core populations. For all these reasons,
speciation is likely to take place in peripheral populations,
making them evolutionarily important (Lesica and Allendorf
1995). Conserving extant peripheral populations is therefore a
unique and integral component of conserving global biodiver-
sity (Lammi et al. 2001; Johannesson and Andre 2006).
Peripheral populations may also exhibit different growth
rates, often associated with the length of the growing season
(characterized by warmer temperatures), which varies at dif-
ferent latitudes (Slaughter et al. 2004). Variation in growth
rate, or capacity for growth, in a species that occurs across a
range of latitudes may provide evidence for countergradient
variation (Conover 1990). Countergradient compensatory
growth occurs when the average effects of genetic and envi-
ronmental influences oppose each other across an environmen-
tal gradient (Conover and Schultz 1995). Countergradient
variation theory holds that some populations of a species at
higher latitudes with shorter growing seasons have a higher
capacity for growth than individuals from populations at lower
latitudes (Conover and Present 1990; Yamahira and Conover
2002). Higher growth capacity at higher latitudes would con-
tribute to increased overwinter survival and may result in a rel-
atively similar size at the end of the growing season for
individuals from higher- and lower-latitude populations (Hurst
2007; see Conover et al. 2009 for a full review of countergra-
dient variation).
Countergradient variation has been identified in a number
of freshwater and marine fishes, such as Striped Bass
Morone saxatilis, Mummichog Fundulus heteroclitus, Ameri-
can Shad Alosa sapidissima (Conover 1990), Lake Sturgeon
Acipenser fulvescens (Power and McKinley 1997), and Atlan-
tic Cod Gadus morhua (Marcil et al. 2006). However, not all
fishes exhibit this trait; Pumpkinseed Lepomis gibbosus,
sticklebacks Gasterosteus spp., and Guppy Poecilia reticulata
show cogradient variation, for which genetic and environmen-
tal influences on phenotype are aligned across a gradient
(Conover et al. 2009). Furthermore, tradeoffs with the higher
capacity for growth may occur in the form of a reduced
swimming ability and higher risk of predation (Billerbeck
et al. 2001; Conover et al. 2005). Countergradient variation
in growth may therefore result in both genetic and morpholog-
ical differences between peripheral and core populations,
further enhancing the conservation value of peripheral
populations.
Although relatively common in the lower Mississippi River
drainage and other areas of the southern United States, the
Spotted Gar Lepisosteus oculatus is poorly studied and its
ecology and status are comparatively unknown in the Great
Lakes Basin. The Spotted Gar is a species of greatest conser-
vation need in the state of Michigan (Michigan Department of
Natural Resources 2005), and there have been no previous
studies focusing on the species within the state. The Spotted
Gar is a native top-level predator (primarily piscivorous), pre-
ferring clear vegetated waters, particularly wetlands and flood-
plain habitat of lakes and large rivers (Suttkus 1963; Trautman
1981; Page and Burr 1991). The species is an important com-
ponent of native food webs, but is threatened, or in some cases
has completely disappeared, due to degradation and loss of
habitat in its range (Trautman 1981; Carman 2002). Because
of its specific habitat preferences, the Spotted Gar may also be
useful as an environmental indicator of aquatic ecosystem
health (USEPA 2007).
The Great Lakes population of Spotted Gars represents the
northern edge of the species’ range and is also completely
838 DAVID ET AL.
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disjunct from the southern U.S. population (Figure 1; Page and
Burr 1991). The species dates back to the early Eocene (48–
55 million years ago; Wiley 1976; Grande 2010) but arrived
in the Great Lakes region relatively recently, approximately
8,000 years ago, when water temperatures began to rise fol-
lowing the Wisconsinan Glaciation (Bailey and Smith 1981;
Hubbs et al. 2004). Spotted Gars in the Great Lakes region are
separated by a large latitudinal distance from the core popula-
tion (approximately 1,231 km between population centers),
and the average length of the growing season is 50% shorter,
approximately 111 d in the Great Lakes region compared with
229 d in the southern United States (NOAA National Climate
Data Center 2011). Because of the large latitudinal distance
and differences in the length of the growing season, variations
in population life history characteristics, such as growth rate,
might be expected. These disjunct Spotted Gar populations
therefore provide an interesting opportunity to investigate
countergradient differences between peripheral and core
populations.
Countergradient variation, or more generally latitudinal
variation in growth, has not been studied in gars (family Lepi-
sosteidae), and the disjunct distribution and ancient ancestry
of the Spotted Gar makes it a unique model species for the
investigation of this phenomenon. To explore the potential dif-
ferences in core and peripheral gar populations in the context
of countergradient variation theory, we compared growth rates
for the first growing season between core and peripheral popu-
lations of the Spotted Gar. Our primary objective was to inves-
tigate differences in life history patterns, specifically growth
rate in the first growing season, between the Great Lakes
(peripheral) and southern United States (core) populations of
Spotted Gars using common garden experiments. Our second
objective was to determine whether any potential variation in
growth rate might be explained by countergradient variation
theory. We hypothesized that Spotted Gars from the northern
peripheral population would exhibit a faster growth rate and
higher capacity for growth at all temperatures compared with
Spotted Gars from the core population.
METHODS
Spotted Gars were acquired from two major sources to rep-
resent the core and peripheral populations. Core population
representatives were collected by colleagues at Nicholls State
University (Thibodaux, Louisiana) in late spring 2009 from
several localities in southeastern Louisiana using experimental
gill nets, and peripheral population representatives were
acquired from several inland lakes in southern Michigan. Fish
from Louisiana were the progeny of wild-caught individuals
from two localities in the Barataria estuary system (Bayou
Chevreuil and Golden Ranch) and one locality in the Terre-
bone estuary system (Chacahoula Swamp) collected in
March–April 2009. Individuals from the core populations
were intermixed in order to reduce potential genetic bias from
a single locality, and the same was done for individuals from
peripheral populations. Adult fish from all core populations
were maintained together in an indoor tank, and spawning was
induced at 21C using Ovaprim (Western Chemical) injections
at a concentration of 0.5 mL/kg body weight. Ovaprim was
introduced via intramuscular injection near the anterior base
of the dorsal fin, and spawning occurred within 24–48 h of
injection. Viable embryos from this spawning event were then
collected from the tank, and approximately 150 specimens
were shipped overnight to the University of Michigan.
Adult peripheral population representatives were collected
in May 2009 from five different inland lake localities in south-
ern Michigan using a boom electrofishing boat. Marble and
East Long lakes are part of the St. Joseph River watershed,
and Round, Carpenter, and Sugarloaf lakes are part of the
Grand River watershed. Adults from peripheral populations
were maintained together in an indoor tank similar to that of
core population fish. Spawning was similarly induced using
Ovaprim but was not as successful; therefore, several adult
fish were stripped of milt and eggs to create approximately
200 embryos. In tables and figures, Spotted Gars from the
core population will be referred to as Louisiana (LA) fish and
those from the peripheral population as Michigan (MI) fish.
Embryos from both populations were raised in separate 38-L
aquaria using aeration and daily 50% water changes to maintain
water quality. A 25-W heater was used to maintain consistent
temperature (21–23C) during the incubation period, as well as
after hatching. Sac-fry and free-swimming larvae were main-
tained in multiple aquaria separated into core or peripheral popu-
lations. Once larvae were zooplanktivorous, they were further
separated into three aquaria per population to better maintain
water quality. Zooplanktivorous larvae were first fed small daph-
nia Daphnia spp. and then larger adult brine shrimp Artemia spp.
Larvae were fed two to three times a day to maintain a constant
supply of food. Upon converting to piscivory, larvae from both
populations were fed small (3.0-cm) Fathead Minnows Pime-
phales promelas. Larvae were further separated roughly based
on size into three aquaria per population to reduce cannibalism.
Due to the limited supply of larvae and the concern of stress-
related mortality due to handling, early life stage fish (sac-fry
FIGURE 1. Distribution of core and peripheral populations of the Spotted
Gar. Note the disjunction between the populations. Modified from Page and
Burr (1991).
COUNTERGRADIENT VARIATION IN SPOTTED GAR GROWTH 839
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and zooplanktivorous stages, approximately 0–60 d) were not
formally measured; length at hatch was estimated from measur-
ing mortalities and photographs of live individuals. To estimate
early life growth rates during the period from 60 to 100 d after
hatch (DAH) preceding experiment 1, 30 individuals from each
population were randomly selected weekly for measurements of
length (0.1 cm) and weight (0.1 g). Mean growth rates (cm/d
and g/d) were then calculated for each population. Once juvenile
Spotted Gars were regularly consuming medium-sized (4.5–
6.0 cm; size range used in experiments) Fathead Minnows, indi-
viduals were randomly selected from each population and placed
into experimental aquaria. All selected individuals were accli-
mated to experimental aquaria for 4–5 d prior to the start of
experiment 1. Additional individuals were maintained in sepa-
rate aquaria (based on population) as replacements if needed and
for experiment 2.
Experiment 1.—To investigate the potential differences in
growth rate under identical temperature and rations, 20 75-L
aquaria were used to house age-0 Spotted Gars from both popu-
lations (ND30 fish from each population). Each aquarium was
divided equally into three compartments using thin fiberglass
screening, which allowed the passage of water but not other fish.
Each compartment housed 1 Spotted Gar (3 per aquarium for a
total of 60 Spotted Gars). Each aquarium also contained an air-
pump-operated sponge filter to maintain water quality and a
50-W heater to maintain a consistent temperature of 22–24C.
The temperature range was selected based on the mean tempera-
tures experienced during the growing season of both populations
(Redmond 1964; Echelle and Riggs 1972; Simon and Wallus
1989; Simon and Tyberghein 1991; S.R.D., personal observa-
tion). To further maintain water quality, 50% of the water was
changed weekly for each tank, with waste material removed via
siphon. Overhead fluorescent lights on electronic timers were
used to maintain a consistent 12-h light and 12-h dark photope-
riod during the experiment. Individual Spotted Gars were fed
Fathead Minnows at near-maximum ration, based on observed
(estimated) consumption during the acclimation period, for the
duration of the experiment: 62 d for core fish and 63 d for
peripheral fish. To maintain near-maximum ration, a small group
of Fathead Minnows (approximately 5.0–7.0 g total mass) was
supplied daily in each experimental compartment; consumed
minnows were replaced and dead minnows were removed to pre-
vent deterioration of water quality. Consumption was not for-
mally recorded but assumed to be equivalent between
populations.
Individual Spotted Gars were removed from the compart-
ments to measure length and weight weekly, as well as at the
beginning and end of the experimental period. Mean length
and weight were used to determine the increase in size (cm/d
and g/d) over the experimental period. One-way analysis of
variance (ANOVA) was used to test for significant differences
in initial and final mean length and weight for both popula-
tions. Analysis of covariance (ANCOVA), with population
and DAH as fixed factors, was used to determine significant
differences in growth rates between populations, if any. We
assumed a linear model for growth during the experimental
period for both populations of Spotted Gars. The increase in
length and weight for each population was plotted versus time
(DAH or days of experiment) and analyzed using linear regres-
sion to generate growth models. Length–weight relationships
were also analyzed (ANOVA, ANCOVA; P<0.05) and used
as a proxy for comparing energy storage between populations.
Experiment 2.—To investigate potential differences in
growth rate between populations at different temperatures,
Spotted Gars from both populations were divided into three
temperature treatments; 16, 23, and 30C, for a total of six
groups (one peripheral group and one core group per tempera-
ture treatment). Each group was comprised of 6 fish, for a total
of 36 fish in the experiment. Fish were randomly selected from
both the individuals used in experiment 1 and the additional
individuals and were all reared under the same temperature
(23C) and feeding regime (near-maximum ration) for at least
30 d prior to beginning the experiment. Due to limits in repli-
cation because of the low numbers of available fish and tanks
(only one replicate of six fish for each population per tempera-
ture treatment), primarily descriptive statistics were used to
analyze experiment 2.
Each group of Spotted Gars was placed in a 190-L fiber-
glass tank containing a stand pipe connected to a large recircu-
lating system for constant water filtration. Temperature was
maintained using 75-W heaters in the control and treatment
group tanks and was monitored daily. All groups were accli-
mated to respective temperature treatments for at least 7 d
prior to beginning the experiment. Spotted Gars in all tanks
were supplied with Fathead Minnows at near-maximum ration
similar to experiment 1 (adjusted for six fish per tank); specific
consumption rates were not measured but were assumed to be
equivalent between populations for each treatment. Photope-
riod was maintained at 12 h light : 12 h dark. Within each
tank individual fish were identified by a single fin clip from
the right or left pectoral fin, right or left pelvic fin, or anal fin
or by no fin clip. Marked fins were reclipped as necessary (due
to fin regeneration) on measurement days over the course of
the experiment. Length and weight of all fish were measured
at the beginning of the experiment, as well as weekly for
5 weeks. The total duration of the experiment was 42 d. Mean
length and weight were determined weekly for both popula-
tions in each treatment, and growth rate was calculated as in
experiment 1.
All statistical analyses were carried out using JMP (2001)
software with significance levels set at aD0.05.
RESULTS
Eggs from both populations hatched 6–7 d after fertiliza-
tion. Hatching success was 70–80% for both populations,
and newly hatched larvae were approximately 1.0 cm in
length and weighed approximately 0.5 g. Larval Spotted
840 DAVID ET AL.
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Gars absorbed their yolk sacs by 6–7 DAH and began feed-
ing on Daphnia and Artemia. Juveniles from both popula-
tions began eating small Fathead Minnows at 35–40 DAH.
The growth rate was similar between populations for length
but was significantly higher for weight during early life
(ANCOVA: sum of squares D67.84, F-ratio D12.17, df D1,
P<0.01) for core Spotted Gars than for peripheral Spotted
Gars held at 23C (Figures 2, 3). Length and weight regression
models explained 96–99% of the variation in the data.
Although both groups of fish were of similar age when switch-
ing to piscivory and acclimating to experimental aquaria,
peripheral fish were significantly smaller than core fish at the
beginning of experiment 1 (one-way ANOVA: P<0.05;
Table 1). The final length and weight of peripheral fish, how-
ever, were significantly greater than for core fish (ANOVA:
P<0.05). Growth rates and least-squares mean lengths and
weights of peripheral Spotted Gars (mean §1 SE, length D
17.40 §0.03 cm, weight D15.40 §0.28 g) were significantly
greater than those of core Spotted Gars (17.10 §0.03 cm,
14.32 §0.34 g; ANCOVA: P<0.01; Table 2). Linear regres-
sion models of growth rates for both populations explained
97–99% of the variation in the data (Figures 4, 5).
At the beginning of experiment 1, peripheral fish had a sig-
nificantly lower weight per unit length than core fish. By the
end of experiment 1, however, peripheral fish had a signifi-
cantly higher weight at length than core fish. Linear regression
analysis and ANCOVA indicated that the change in weight–
length ratios was significantly different between peripheral
(higher rate) and core fish (lower rate) over the course of
experiment 1 (Figure 6). Although consumption was not for-
mally recorded, fish from both populations typically consumed
their allotted ration on a daily basis during the experimental
period.
In experiment 2, the ending size (length and weight) and
growth rates of Spotted Gars across all temperature treatments
were lowest at 16C, higher at 23C, and highest at 30C
(Table 3; Figure 7). At 16C, the coolest treatment, fish from
both populations exhibited very small increases in length
(peripheral fish D0.02 cm, core fish D0.10 cm) and decreases
in weight (peripheral fish 1.18 g, core fish 0.38 g)
over the 42-d period. Clipped fins (used to identify individual
fish) did not regenerate and visually estimated consumption of
Fathead Minnows was very low compared with the other tem-
perature treatments (i.e., the daily ration of minnows was not
fully consumed). In contrast, fish in the 23C and 30C treat-
ments required frequent reclipping of marked fins, as well as
much more frequent replacement of Fathead Minnows. As in
experiment 1, fish from both populations typically consumed
FIGURE 2. Comparison of early life stage (period prior to the start of experiment 1) length at age of Spotted Gars from core (LA) and peripheral (MI) popula-
tions that were held at 23C(ND30 fish/population). Larval fish from both populations hatched at approximately 1.0 cm in length. Linear regression models
(dashed line DLA, solid line DMI) and R
2
-values were also calculated.
COUNTERGRADIENT VARIATION IN SPOTTED GAR GROWTH 841
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their allotted ration on a daily basis during the experimental
period.
The peripheral fish in both the 23C and 30C treatments
grew faster and larger than the core fish (Figure 8). Maximum
growth for both groups occurred at the highest temperature
treatment, while the 16C treatment appeared to be at or
near the point at which growth ceased in both populations of
Spotted Gars.
DISCUSSION
We hypothesized that Spotted Gars from two disjunct popu-
lation segments would exhibit latitudinal compensation in
growth similar to several other fish species (Conover et al.
2009) and that under common environmental conditions fish
from a higher latitude would grow faster than those from a
lower latitude. Our experiments showed that in a common
environment simulating periods within the first growing sea-
son, the Spotted Gars from the peripheral population had a sig-
nificantly higher growth rate than those from the core
population, suggesting that important genetic and physiologi-
cal differences exist between the two population groups.
Although the lack of treatment replication limits the statistical
analyses of experiment 2, results suggest that peripheral Spot-
ted Gars achieved a higher growth rate than core population
fish even at warmer temperatures and that both populations
had similar thermal minima for growth. Both experiments
taken together provide strong evidence for countergradient
variation in the growth rate of Spotted Gars.
FIGURE 3. Comparison of early life stage (period prior to the start of experiment 1) weight at age of Spotted Gars from core (LA) and peripheral (MI) popula-
tions that were held at 23C(ND30 fish/population). Larval fish from both populations hatched at approximately 0.5 g. Exponential regression models (dashed
line DLA, solid line DMI) and R
2
-values were also calculated; DAH Ddays after hatch.
TABLE 1. Mean length (cm) and weight (g) at initiation and completion of
experiment 1, along with total growth (final length or weight – initial length or
weight), growth rate (cm/day or g/day), and descriptive statistics for core (LA)
and peripheral (MI) populations of Spotted Gars (ND30 fish/population).
Experimental durations were 62 (LA) and 63 (MI) days.
Population
MI LA ANOVA
Measurements Mean SD Mean SD df F-Ratio P-Value
Initial length 14.29 1.85 15.56 1.55 1, 58 8.36 <0.01
Final length 20.06 1.64 18.24 1.45 1, 58 20.57 <0.01
Total growth 5.77 2.68
Growth rate 0.09 0.04
Initial weight 7.50 3.01 10.74 3.21 1, 58 16.23 <0.01
Final weight 24.09 6.84 17.53 4.12 1, 58 20.26 <0.01
Total growth 16.59 6.79
Growth rate 0.26 0.11
842 DAVID ET AL.
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As in the Atlantic Silverside Menidia menidia, the model
species used to investigate countergradient variation in growth
by Conover and Present (1990) (see also Conover 1992; Pres-
ent and Conover 1992), Spotted Gars begin spawning at
approximately the same temperature (23C) but later in the
year with increasing latitude (Redmond 1964; Holt 1973;
Trautman 1981; Becker 1983; Snedden 1999). Conover
(1990) also noted that later initiation of spawning and earlier
onset of winter resulted in a much shorter growing season
at higher latitudes. Although the length of the growing
season decreases as latitude increases, the mean size at the end
of the first growing season does not decrease with increasing
latitude for several fish species (Conover et al. 2009). There-
fore populations of these species at higher latitudes are able
to compensate for shorter growing seasons by evolving
faster growth rates than lower-latitude populations (Conover
1992).
Observed growth rates for Spotted Gars were higher in the
peripheral population than in the core population over a simu-
lated growing season (experiment 1). This result provides further
TABLE 2. Results of F-tests for the equality of slopes from length–day after hatch (DAH) and weight–DAH relationships for Spotted Gars between peripheral
and core populations. The degrees of freedom (df), sum of squares (SS), F-ratios, and P-values are also reported.
Variable Source df SS F-ratio P-value
Length DAH 1 26.94 3,992.6 <0.01
Population 1 0.32 46.94 <0.01
DAH £population 1 3.92 580.93 <0.01
Weight DAH 1 220.19 317.66 <0.01
Population 1 4.25 6.13 <0.01
DAH £population 1 46.39 66.93 <0.01
Weight : length Length 1 11,306.69 3,921.19 <0.01
Population 1 78.74 27.31 <0.01
Length £population 1 38.74 38.75 <0.01
FIGURE 4. Increase in length over time for Spotted Gars from core (LA) and peripheral (MI) populations that were held at 23C in experiment 1
(ND30 fish/population). Linear regression models (dashed line DLA, solid line DMI) and R
2
-values were also calculated; DAH Ddays after hatch.
COUNTERGRADIENT VARIATION IN SPOTTED GAR GROWTH 843
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support of countergradient variation when experimental growth
rates are applied to the estimated respective length of the grow-
ing season, resulting in larger peripheral population fish or simi-
lar-sized individuals between the populations (peripheral:
0.09 cm/d £111 d D9.99 cm, 0.26 g/d £111 d D28.86 g;
core: 0.04 cm/d £229 d D9.16 cm, 0.11 g/d £229 d D
25.19 g); albeit this is a very coarse estimate (Conover et al.
2009). Future studies incorporating field-based length-at-age
and length-of-growing-season estimates (such as hard structures,
older individuals, and thermal opportunity for growth by degree-
days; Power and McKinley 1997; David 2012) for multiple pop-
ulations may further elucidate latitudinal differences in growth
rates.
Differences in growth rate may be indicative of other inter-
esting eco-evolutionary dynamics between core and peripheral
populations of Spotted Gars (David 2012), such as differences
in life history patterns, as well as morphological and genetic
variation (Wright et al. 2012; Glass et al., in press). From an
evolutionary perspective, our results suggest that rapid adapta-
tion in growth rate has occurred even in relatively slowly
evolving fishes, such as gars (Wiley 1976; Conover et al.
2009; Grande 2010; Carlson et al. 2011). The Spotted Gar, a
warmwater species, entered the Great Lakes region via con-
nections to the Mississippi River drainage (southern refugium)
following the last glaciation no more than 8,000 years ago
(Bailey and Smith 1981; Hocutt and Wiley 1986). Therefore
the adaptation of growth rate to the length of the growing sea-
son must be a relatively recent evolutionary development.
Similarly, Mach et al. (2011) showed that in Atlantic Silver-
sides, another species that expanded northward postglaciation
from a single southern refugium, regional adaptation (e.g.,
countergradient variation) and phenotypic divergence devel-
oped since the last glaciation. Using Pacific salmon Oncorhyn-
chus spp., Carlson et al. (2011) showed that shifts in body size
due to selection over even a single generation can have large
and lasting evolutionary impacts on both species and
ecosystems.
The scope of our study was limited to two of several region-
ally distinct populations (core and peripheral) of Spotted Gars;
including more populations in future experiments may provide
a better picture of the gradient in growth rate with increasing
latitude. Despite this limitation, our study populations did rep-
resent a natural break in the distribution of Spotted Gars, in
that the species is completely disjunct between the Great
Lakes and Mississippi River basins (Page and Burr 1991);
therefore, these comparisons are realistic if not comprehen-
sive. The core population does span a greater latitudinal range
than the peripheral population (approximately 1,550 km com-
pared with 220 km); therefore, growth rate comparisons
among fish from multiple core populations are recommended.
FIGURE 5. Increase in weight over time for Spotted Gars from core (LA) and peripheral (MI) populations that were held at 23C in experiment 1 (ND30
fish/population). Linear regression models (dashed line DLA, solid line DMI) and R
2
-values were also calculated; DAH Ddays after hatch.
844 DAVID ET AL.
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Detailed measurements of the early life stages preceding pisci-
vory (e.g., zooplanktivorous stage) were not formally made in
our experiments; however, the growth rate for weight observed
during these early stages was higher in core than in peripheral
populations. Once the piscivorous stage was reached, the
growth rate was higher in peripheral than in core populations.
Mittelbach and Persson (1998) found that growth rates of
piscivorous fishes (including gars) greatly increased between
the zooplanktivorous and piscivorous stages. Although growth
rates were significantly different between populations at early
life stages, differences in growth rate were comparatively
much greater when Spotted Gars switched to piscivory.
Experiments comparing gars at prepiscivorous stages would
help clarify early life stage differences between core and
peripheral populations.
Our study did not specifically measure consumption rates or
ration; however, fish from both populations typically con-
sumed their allotted ration on a daily basis in both experiments
(with the exception of the lowest temperature treatment in
experiment 2), suggesting that consumption rates were similar
between populations in our study. Present and Conover (1992)
showed that at excess ration, a higher growth rate in Atlantic
Silversides from a higher latitude could be explained by
genetic variation in consumption rate and gross growth effi-
ciency compared with a lower-latitude population. We
assumed consumption rates to be similar between populations
in our experiments; complete consumption of the daily ration
by both populations supports this, and higher conversion effi-
ciency and other metabolic rates (Conover and Schultz 1995)
may similarly explain differences in Spotted Gar growth rates
between core and peripheral populations. To better understand
the drivers of the observed differences in growth rate, future
studies comparing metabolic rates of peripheral and core Spot-
ted Gars are recommended, as well as exploration of any
potential molecular basis.
Although countergradient variation has been observed in a
variety of ectotherms, most frequently in fishes, it has not pre-
viously been observed in gars. Furthermore, our study is the
first to use common garden experiments to test for latitudinal
variation in a nonteleost fish, an understudied group in such
investigations, often because of their typically late maturation
and long generation time (Ferrara 2001; Mendoza Alfaro et al.
2008) compared with teleosts in similar studies (Conover and
Present 1990; Schultz et al. 1996; Arendt and Wilson 1997;
Power and McKinley 1997; Conover et al. 2009; Baumann
and Conover 2011). Our results suggest that countergradient
variation may be important in other evolutionarily and eco-
nomically significant nonteleost species (i.e., lungfishes [sub-
class Dipnoi], sturgeons [family Acipenseridae], and Alligator
Gar Atractosteus spatula).
FIGURE 6. Mean weight–length ratios over time for Spotted Gars from the core (LA) and peripheral (MI) populations that were held at 23C in experiment 1
(ND30 fish/population). Linear regression models (dashed line DLA, solid line DMI) and R
2
-values were also calculated; DAH Ddays after hatch.
COUNTERGRADIENT VARIATION IN SPOTTED GAR GROWTH 845
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The countergradient variation in the growth of Spotted Gars
may also have implications for the species’ response to future
climate change and to opportunities for range expansion.
Using the weak latitudinal temperature gradient of Topsmelt
Atherinops affinis as a proxy for the gradual effects of climate
change, Baumann and Conover (2011) showed that two spe-
cies, Atlantic Silversides and Topsmelt, each experiencing
very different latitudinal temperature gradients, still exhibited
countergradient variation in growth. Their study indicated that
ectotherms have evolved growth adaptations to even weak cli-
mate gradients and that a poleward migration of genotypes
will be a likely result of an increasingly warmer climate. As a
warmwater species exhibiting countergradient variation, Spot-
ted Gars would likely successfully increase their range north-
ward with gradual increases in temperature.
Peripheral populations are important in terms of a species’
ecology, biogeography, and evolution but also from a conser-
vation perspective (Scudder 1989; Conover et al. 2009).
Because populations of species at the end of their range may
be more susceptible to perturbation, identifying these at-risk
populations is important (Glass et al., in press). Observed dif-
ferences (or lack thereof) in the size of individuals across a
range of latitudes may help identify at-risk populations. Com-
mon garden experiments, coupled with age–growth and
genetic analyses could confirm the existence of countergra-
dient variation and unique populations (David 2012). Further,
in efforts to restore declining populations of species, individu-
als are often transplanted from one population to another
(Fischer and Lindenmayer 2000); because countergradient
variation may not be readily observable, these transplants
should be made with caution to avoid the stocking of maladap-
tive genotypes into new environments (Conover et al. 2009).
Previous studies have shown that in aquatic systems, spe-
cies at higher trophic levels are at higher risk of extirpation
and are more frequently lost than those at lower trophic levels,
in part because of their relatively small population sizes
TABLE 3. Mean length (cm) and weight (g) at initiation and completion of experiment 2, along with total growth (final length or weight – initial length or
weight), growth rate (cm/day or g/day), and descriptive statistics for core and peripheral populations of Spotted Gars at three different temperature treatments
(ND6 fish/population in each treatment). Experimental duration was 42 d.
Peripheral Core
Experimental
temperature (C) Measurement Mean SD Mean SD
Length
16 Initial length 21.07 1.03 19.17 1.26
Final length 21.08 0.97 19.27 1.37
Total growth 0.02 0.10
Growth rate <0.01 <0.01
23 Initial length 20.75 0.82 19.85 2.70
Final length 23.52 1.12 21.33 2.72
Total growth 2.77 1.48
Growth rate 0.07 0.04
30 Initial length 22.60 2.62 20.72 0.95
Final length 25.50 1.72 23.15 1.11
Total growth 2.90 2.43
Growth rate 0.07 0.06
Weight
16 Initial weight 27.73 4.73 21.77 4.92
Final weight 26.55 4.31 21.38 5.02
Total growth ¡1.18 ¡0.38
Growth rate ¡0.03 ¡0.01
23 Initial weight 24.63 3.26 23.73 9.82
Final weight 37.12 6.70 30.05 13.97
Total growth 12.48 6.32
Growth rate 0.30 0.15
30 Initial weight 32.50 11.60 25.27 4.48
Final weight 51.97 10.44 36.32 6.48
Total growth 19.47 11.05
Growth rate 0.46 0.26
846 DAVID ET AL.
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(Lande 1993; Petchey et al. 2004). Piscivorous fishes, there-
fore, may be particularly vulnerable amid the ongoing biodi-
versity crisis. Furthermore, nongame piscivorous species (e.g.,
gars and Bowfin Amia calva) may be even more at risk due to
their poorly studied ecology, their perceived low economic
value, and the higher priority given to propagation and man-
agement of game species (centrarchids, percids, esocids), with
the latter often leading to the destruction of both nongame
FIGURE 7. Changes in mean length and weight for Spotted Gars from peripheral (solid line) and core (dashed line) populations at three temperature treatments
in experiment 2: (A) 16C, (B) D23C, and (C) D30C(ND6 fish/population in each treatment; experimental duration D42 d). Note the change in the y-axis
scale for length and weight among figures.
COUNTERGRADIENT VARIATION IN SPOTTED GAR GROWTH 847
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individuals and habitat (Scarnecchia 1992). Our study pro-
vides evidence of the unique characteristics of the peripheral
population of Spotted Gars and provides more evidence for
the general argument that understanding and protecting
peripheral populations should be a key component of our pro-
grams to conserve natural biodiversity.
ACKNOWLEDGMENTS
Funding and support for this project were provided in part by
the University of Michigan School of Natural Resources and Envi-
ronment, Michigan Department of Natural Resources, National
Oceanic and Atmospheric Administration Great Lakes Environ-
mental Research Laboratory, North American Native Fishes
Association, and Fish Doctors Ypsilanti. This is National Oceanic
and Atmospheric Administration, Great Lakes Environmental
Research Laboratory contribution 1759. We thank Quenton Fon-
tenot and Allyse Ferrara of Nicholls State University for their
expertise on gar spawning, as well as for the gar embryos from
core populations. We also thank Brad Utrup, Madison Schaeffer,
and Joe Nohner for assistance with common garden experiments
and Barry OConnor for manuscript review.
REFERENCES
Arendt, J. D., and D. S. Wilson. 1997. Optimistic growth: competition and an
ontogenetic niche-shift select for rapid growth in Pumpkinseed Sunfish
(Lepomis gibbosus). Evolution 51:1946–1954.
Baumann, H., and D. O. Conover. 2011. Adaptation to climate change: con-
trasting patterns of thermal-reaction-norm evolution in Pacific versus Atlan-
tic silversides. Proceedings of the Royal Society B 278:2265–2273.
Bailey, R. M., and G. R. Smith. 1981. Origin and geography of the fish fauna
of the Laurentian Great Lakes basin. Canadian Journal of Fisheries and
Aquatic Sciences 38:1539–1561.
Becker, G. C. 1983. Fishes of Wisconsin. University of Wisconsin Press,
Madison.
Berrigan, D., and J. C. Koella. 1994. The evolution of reaction norms: simple mod-
els for age and size at maturity. Journal of Evolutionary Biology 7:549–566.
Billerbeck, J. M., T. E. Lankford, and D. O. Conover. 2001. Evolution of
intrinsic growth and energy acquisition rates: I. tradeoffs with swimming
performance in Menidia menidia. Evolution 55:1863–1872.
Carlson, S. M., T. P. Quinn, and A. P. Hendry. 2011. Eco-evolutionary dynam-
ics in Pacific salmon. Heredity 103:438–447.
Carman, S. M. 2002. Special animal abstract for Lepisosteus oculatus (Spotted
Gar). Michigan Natural Features Inventory, Lansing.
Channell, R., and M. V. Lomolino. 2000. Trajectories to extinction: spatial
dynamics of the contraction of geographical ranges. Journal of Biogeogra-
phy 27:169–179.
Conover, D. O. 1990. The relation between capacity for growth and length of
growing season: evidence for and implications of countergradient variation.
Transactions of the American Fisheries Society 119:416–430.
Conover, D. O. 1992. Seasonality and the scheduling of life history at different
latitudes. Journal of Fish Biology 41:161–178.
Conover, D. O., S. A. Arnott, M. R. Walsh, and S. B. Munch. 2005. Darwinian
fishery science: lessons from the Atlantic Silverside (Menidia menidia).
Canadian Journal of Fisheries and Aquatic Sciences 62:730–737.
Conover, D. O., T. A. Duffy, and L. A. Hice. 2009. The covariance between
genetic and environmental influences across ecological gradients. Annals of
the New York Academy of Sciences 1168:100–129.
Conover, D. O., and T. M. C. Present. 1990. Countergradient variation in
growth rate: compensation for length of the growing season among Atlantic
Silversides from different latitudes. Oecologia 83:316–324.
Conover, D. O., and E. T. Schultz. 1995. Phenotypic similarity and the evolu-
tionary significance of countergradient variation. Trends in Ecology and
Evolution 10:248–252.
David, S. R. 2012. Life history, growth, and genetic diversity of the Spotted
Gar Lepisosteus oculatus from peripheral and core populations. Doctoral
dissertation. University of Michigan, Ann Arbor.
Echelle, A. A., and C. D. Riggs. 1972. Aspects of the early life history of gars
(Lepisosteus) in Lake Texoma. Transactions of the American Fisheries
Society 101:106–112.
Ferrara, A. M. 2001. Life-history strategy of Lepisosteidae: implications for
the conservation and management of Alligator Gar. Doctoral dissertation.
Auburn University, Auburn, Alabama.
Fischer, J., and D. B. Lindenmayer. 2000. An assessment of the published
results of animal relocations. Biological Conservation 96:1–11.
Foster, S. J., and A. C. J. Vincent. 2004. Life history and ecology of seahorses:
implications for conservation and management. Journal of Fish Biology
65:1–61.
Garner, A., J. L. Rachlow, and J. F. Hicks. 2005. Patterns of genetic diversity
and its loss in mammalian populations. Conservation Biology 19:1215–1221.
Glass, W. R., R. P. Walter, D. D. Heath, N. E. Mandrak, and L. D. Corkum. In
press. Genetic structure and diversity of Spotted Gar (Lepisosteus oculatus)
at its northern range edge: implications for conservation. Conservation
Genetics. DOI: 10.1007/s10592-015-0708-2.
Grande, L. 2010. An empirical synthetic pattern study of gars (Lepisostei-
formes) and closely related species, based mostly on skeletal anatomy. The
FIGURE 8. Mean daily growth rates for (A) length and (B) weight of Spotted
Gars from core (LA) and peripheral (MI) populations at three temperature
treatments (16, 23, and 30C; ND6 fish/population in each treatment) in
experiment 2 (experimental duration D42 d). Error bars indicate §1 SE.
848 DAVID ET AL.
Downloaded by [107.199.220.85] at 15:00 29 June 2015
resurrection of Holostei. Copeia 2010(American Society of Ichthyologists
and Herpetologists Special Publication 6):778.
Heibo, E., C. Magnhagen, and L. A. Vollestad. 2005. Latitudinal variation in
life-history traits in Eurasian Perch. Ecology 86:3377–3386.
Helfman, G. S. 2007. Fish conservation. Island Press, Washington, D.C.
Hocutt, C. H., and E. O. Wiley. 1986. The zoogeography of North American
freshwater fishes. Wiley, New York.
Holt, R. 1973. Age and growth, length-weight relationship, condition coeffi-
cient, and feeding habits of Spotted Gar, Lepisosteus oculatus (Winchell),
within the Kentucky waters of Kentucky Reservoir. Master’s thesis. Murray
State University, Murray, Kentucky.
Hooper, D. U., F. S. Chapin III, J. J. Ewel, A. Hector, P. Inchausti, S. Lavorel,
J. H. Lawton, D. M. Lodge, M. Loreau, S. Naeem, B. Schmid, H. Setala, A.
J. Symstad, J. Vandermeer, and D. A. Wardle. 2005. Effects of biodiversity
on ecosystem functioning: a consensus of current knowledge. Ecological
Monographs 75:3–35.
Hubbs, C. L., K. F. Lagler, and G. R. Smith. 2004. Fishes of the Great Lakes
region, revised edition. University of Michigan Press, Ann Arbor.
Hurst, T. P. 2007. Causes and consequences of winter mortality in fishes. Jour-
nal of Fish Biology 71:315–345.
JMP. 2001. JMP, version 4. SAS Institute, Cary, North Carolina.
Johannesson, K., and C. Andre. 2006. Life on the margin: genetic isolation and
diversity loss in a peripheral marine ecosystem, the Baltic Sea. Molecular
Ecology 15:2013–2029.
Jones, B., C. Gliddon, and J. E. G. Good. 2001. The conservation of variation
in geographically peripheral populations: Lloydia serotina (Liliaceae) in
Britain. Biological Conservation 101:147–156.
Kyle, C. J., and C. Strobeck. 2002. Connectivity of peripheral and core
populations of North American wolverines. Journal of Mammalogy
83:1141–1150.
Kynard, B. 1997. Life history, latitudinal patterns, and status of the Shortnose
Sturgeon, Acipenser brevirostrum. Environmental Biology of Fishes
48:319–334.
Lammi, A., P. Siikamaki, and K. Mustajarvi. 2001. Genetic diversity, popula-
tion size, and fitness in central and peripheral populations of a rare plant
Lychnis viscaria. Conservation Biology 13:1069–1078.
Lande, R. 1993. Risks of population extinction from demographic and envi-
ronmental stochasticity and random catastrophes. American Naturalist
142:911–927.
Lardies, M. A., L. D. Bacigalupe, and F. Bozinovic. 2004. Testing the meta-
bolic cold adaptation hypothesis: an intraspecific latitudinal comparison in
the common wood louse. Evolutionary Ecology Research 6:567–578.
Latta, W. C. 2003. Distribution and abundance of Michigan fishes collected
1993–2001. Michigan Department of Natural Resources, Fisheries Research
Report, Ann Arbor.
Lee, H., D. DeAngelis, and H. Koh. 1998. Modeling spatial distribution of the
unionid mussels and the core-satellite hypothesis. Water, Science, and
Technology 38:73–79.
Lesica, P., and F. W. Allendorf. 1995. When are peripheral populations valu-
able for conservation? Conservation Biology 9:753–760.
Luck, G. W., G. C. Daily, and P. R. Ehrlich. 2003. Population diversity and
ecosystem services. Trends in Ecology and Evolution 18:331–336.
Mach, M. E., E. J. Sbrocco, L. A. Hice, T. A. Duffy, D. O. Conover, and P. H.
Barber. 2011. Regional differentiation and post-glacial expansion of the
Atlantic Silverside, Menidia menidia, an annual fish with high dispersal
potential. Marine Biology 158:515–530.
Marcil, J., D. P. Swain, and J. A. Hutchings. 2006. Genetic and environmental
components of phenotypic variation in body shape among populations of
Atlantic Cod (Gadus morhua L.). Biological Journal of the Linnean Society
88:351–365.
Mendoza Alfaro, R., C. A. Gonzales, and A. M. Ferrara. 2008. Gar biology and
culture: status and prospects. Aquaculture Research 39:748–763.
Michigan Department of Natural Resources. 2005. Species of greatest conser-
vation need. Michigan’s wildlife action plan. State of Michigan, Lansing.
Mittelbach, G. G., and L. Persson. 1998. The ontogeny of piscivory and its
ecological consequences. Canadian Journal of Fisheries and Aquatic
Sciences 55:1454–1465.
Munch, S. B., M. Mangel, and D. O. Conover. 2003. Quantifying natural selec-
tion on body size from field data: winter mortality in Menidia menidia. Ecol-
ogy 84:2168–2177.
NOAA (National Oceanic and Atmospheric Administration) National Climate
Data Center. 2011. U.S. climate normals 1971–2000. Available: http://cdo.
ncdc.noaa.gov/cgi-bin/climatenormals/climatenormals.pl. (February 2011).
Page, L. M., and B. M. Burr. 1991. A field guide to freshwater fishes.
Houghton Mifflin, Boston.
Petchey, O. L., A. L. Downing, G. G. Mittelbach, L. Persson, C. F. Steiner, P.
H. Warren, and G. Woodward. 2004. Species loss and structure and func-
tioning of multitrophic aquatic systems. Oikos 104:467–478.
Power, M., and R. S. McKinley. 1997. Latitudinal variation in Lake Sturgeon
size as related to the thermal opportunity for growth. Transactions of the
American Fisheries Society 126:549–558.
Present, T. M., and D. O. Conover. 1992. Physiological basis of latitudinal
growth differences in Menidia menidia: variation in consumption or effi-
ciency? Functional Ecology 6:23–31.
Redmond, L. C. 1964. Ecology of the Spotted Gar (Lepisosteus oculatus Win-
chell) in southeastern Missouri. Master’s thesis. University of Missouri,
Columbia.
Scarnecchia, D. L. 1992. A reappraisal of gars and bowfins in fishery manage-
ment. Fisheries 17(5):6–12.
Schultz, E. T., K. E. Reynolds, and D. O. Conover. 1996. Countergradient var-
iation in growth among newly hatched Fundulus heteroclitus: geographic
differences revealed by common-environment experiments. Functional
Ecology 10:366–374.
Scudder, G. G. E. 1989. The adaptive significance of marginal populations: a
general perspective. Canadian Special Publication of Fisheries and Aquatic
Sciences 105:180–185.
Simon, T. P., and E. J. Tyberghein. 1991. Contributions to the early life history
of the Spotted Gar, Lepisosteus oculatus Winchell, from Hatchet Creek,
Alabama. Transactions of the Kentucky Academy of Science 52:124–131.
Simon, T. P., and R. Wallus.1989. Contributions to the early life histories of
gar (Actinopterygii: Lepisosteidae) in the Ohio and Tennessee River basins
with emphasis on larval development. Transactions of the Kentucky Acad-
emy of Science 50:59–71.
Slaughter, J. E. IV, R. A. Wright, and D. R. DeVries. 2004. The effects of age-
0 body size and the predictive ability of a Largemouth Bass bioenergetics
model. Transactions of the American Fisheries Society 133:279–291.
Slaughter, J. E. IV, R. A. Wright, and D. R. DeVries. 2008. Latitudinal influ-
ence on first-year growth and survival of Largemouth Bass. North American
Journal of Fisheries Management 28:993–1000.
Snedden, G. A., W. E. Kelso, and D. A. Rutherford. 1999. Diel and seasonal
patterns of Spotted Gar movement and habitat use in the lower Atchafalaya
River basin, Louisiana. Transactions of the American Fisheries Society
128:144–154.
Stearns, S. C., and J. C. Koella. 1986. The evolution of phenotypic plasticity in
life-history traits: predictions of reaction norms for age and size at maturity.
Evolution 40:893–913.
Suttkus, R. D. 1963. Order Lepisostei. Pages 61–88 in H. B. Bigelow, C. M.
Breeder, Y. H. Olsen, D. M. Cohen, W. C. Schroeder, G. W. Mead, L. P.
Schultz, D. Merriman, and J. Tee-Van, editors. Fishes of the western North
Atlantic; part three, soft-rayed fishes. Yale University, Memoir Sears Foun-
dation for Marine Research 1, New Haven, Connecticut.
Trautman, M. B. 1981. The Fishes of Ohio, revised edition. Ohio State Univer-
sity Press, Columbus.
United Nations. 1992. Convention on biological diversity. United Nations,
New York. Available: http://www.cbd.int/. (June 2015).
USEPA (U.S. Environmental Protection Agency). 2007. Biological indicators
of watershed health. Available: www.epa.gov/bioiweb1/html/fish_indicators.
html. (August 2008).
COUNTERGRADIENT VARIATION IN SPOTTED GAR GROWTH 849
Downloaded by [107.199.220.85] at 15:00 29 June 2015
Wiley, E. O. 1976. The phylogeny and biogeography of fossil and recent gars
(Actinopterygii: Lepisosteidae). University of Kansas Museum of Natural
History Miscellaneous Publication 64.
Wilson, B. S., and D. E. Cooke. 2004. Latitudinal variation in rates of
overwinter mortality in the lizard Uta stansburiana. Ecology 85:3406–
3417.
Wisely, S. M., S. W. Buskirk, G. A. Russell, K. B. Aubry, and W. J. Zielinski.
2004. Genetic diversity and structure of the fisher (Martes pennanti)ina
peninsular and peripheral metapopulation. Journal of Mammalogy 85:640–
648.
Wright, J. J., S. R. David, and T. J. Near. 2012. Gene trees, species trees, and
morphology converge on a similar phylogeny of living gars (Actinopterygii:
Holostei: Lepisosteidae), an ancient clade of ray-finned fishes. Molecular
Phylogenetics and Evolution 63:848–856.
Yakimowski, S. B., and C. G. Eckert. 2007. Threatened peripheral populations
in context: geographical variation in population frequency and size and sexual
reproduction in a clonal woody shrub. Conservation Biology 21:811–822.
Yamahira, K., and D. O. Conover. 2002. Intra- vs. interspecific latitudinal vari-
ation in growth: adaptation to temperature or seasonality? Ecology
83:1252–1262.
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... In addition to the importance of submerged vegetation, several other aquatic habitat conditions are known to influence the early life stages of spotted gar. For instance, water temperature affects the early development of YOY spotted gar, with higher growth rates observed following exposure to higher temperatures (23-30 • C) (David et al. 2015;Long et al. 2020). The final hatching success of fertilized eggs was reduced by 24% in experiments with exposure to mildly turbid (5 NTU) waters, suggesting turbidity has the potential to contribute to population declines (Gray et al. 2012). ...
... Water temperature (de Roth 1973;David et al. 2015;Long et al. 2020), site depth (Redmond 1964;Tyler and Granger 1984;Love 2004;Glass et al. 2012), turbidity (Gray et al. 2012), distance from shore (Glass et al. 2012), and SAV presence (Love 2004;Glass et al. 2012;Long et al. 2020) were used as predictor variables in multiple logistic regression models to determine which set of habitat features were most associated with the detection of YOY spotted gar across all sites using models of the form (Agresti 2002): ...
... YOY spotted gar habitat use was also found to depend on other habitat conditions. The use of warmer water temperatures noted here aligns with the findings from laboratory studies using YOY spotted gar, which have suggested preferred temperatures in the 23.8 • C (Long et al. 2020) to 30 • C (David et al. 2015) range. The occurrence of YOY spotted gar in the warmer range of water temperatures (22.5-25 • C) noted here may also reflect the water temperatures used by spawning adults: 21-26 • C (Cudmore-Vokey and Minns 2002) and 20-23 • C (Glass et al. 2012). ...
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The young-of-year (YOY) habitat of many fishes listed under the Species at Risk Act (SARA) is poorly described, yet identifying critical habitat is essential to ensure species recovery. Past research on the Endangered Spotted Gar (Lepisosteus oculatus, (Winchell 1864)) in Canada has focused on the habitat use of adults and juveniles, but little is known about the occurrence and habitat use of YOY. Dip net and aquatic habitat sampling were performed in nearshore (lakefront, agricultural drain), mid-channel (agricultural drain), and offshore sites within Rondeau Bay to determine the fine-scale habitat occupancy patterns of age-0 Spotted Gar. Habitat preference analysis indicated YOY Spotted Gar strongly preferred shallow (0.5 – 1.0 m), vegetated, nearshore (lakefront and agricultural drain) habitat and avoided offshore habitat. An association between submerged aquatic vegetation (SAV) and fish size was also found, as dependence on SAV diminished as total length increased. Our study represents the first capture and assessment of habitat associations of early-stage YOY Spotted Gar in Canada. Given our findings, management efforts should focus on protecting the vegetated nearshore habitat in Rondeau Bay and other occupied locations in Lake Erie to ensure the long-term persistence of Spotted Gar in Canada.
... Gars (family: Lepisosteidae) are a basal lineage of fishes that are widespread in central and eastern North America and throughout Central America (Echelle and Grande 2014). Gars are native, large-bodied, top-level piscivores, and are important components of aquatic food webs (David et al. 2015). Nonetheless, these fishes have long been viewed as nuisance species, and as such, many aspects of their biology remain understudied (Scarnecchia 1992). ...
... Populations of several species within Lepisosteidae have declined as a result of habitat loss and removal efforts and now face conservation issues (Scarnecchia 1992, Alfaro et al. 2008, Staton et al. 2012, NatureServe 2016. Spotted gar (Lepisosteus oculatus), while globally secure, is a species of conservation concern at the northern edge of its range and is critically imperiled in Canada (Glass et al. 2011, Staton et al. 2012, David et al. 2015, NatureServe 2016, Ontario Ministry of Natural Resources and Forestry 2016 and Kansas, Ohio, and Pennsylvania and is thought to be extirpated in New Mexico (NatureServe 2016). ...
... Research efforts on conservation for the spotted gar and other species of Lepisosteidae have mostly been directed toward understanding population dynamics. To date, most studies have focused on adults (Love 2004, Glass et al. 2011, Staton et al. 2012, David et al. 2015, but little is known about the early life history of gars. The recovery strategy for spotted gar in Canada emphasized the importance of early life history on population growth rates (Staton et al. 2012, Ontario Ministry of Natural Resources andForestry 2016). ...
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Accurate age and growth information is essential in successful management of fish populations and for understanding early life history. We validated daily increment deposition, including the timing of first ring formation, for spotted gar (Lepisosteus oculatus) through 127 days post hatch. Fry were produced from hatchery-spawned specimens, and up to 10 individuals per week were sacrificed and their otoliths (sagitta, lapillus, and asteris-cus) removed for daily age estimation. Daily age estimates for all three otolith pairs were significantly related to known age. The strongest relationships existed for measurements from the sagitta (r ² = 0.98) and the lapillus (r ² = 0.99) with asteriscus (r ² = 0.95) the lowest. All age prediction models resulted in a slope near unity, indicating that ring deposition occurred approximately daily. Initiation of ring formation varied among otolith types, with deposi-tion beginning 3, 7, and 9 days for the sagitta, lapillus, and asteriscus, respectively. Results of this study suggested that otoliths are useful to estimate daily age of spotted gar juveniles; these data may be used to back calculate hatch dates, estimate early growth rates, and correlate with environmental factor that influence spawning in wild populations. This early life history information will be valuable in better understanding the ecology of this species.
... As noted by Scarnecchia (1992), work prior to 2000 focused largely on diet due to long-held beliefs that gars were unequivocally detrimental to game fish populations. As a result, basic information on life history and ecology of gars has lagged far behind our knowledge of many other fishes (Buckmeier et al. 2013;Binion et al. 2015;David et al. 2015;Smylie et al 2015;David et al. 2018). ...
... Alternatively, adult fish may be collected for each spawn (Mendoza et al. 2008;Castillo et al. 2015;Armstrong et al. this issue). Induced spawns typically occur during the natural spawning season, the timing of which varies by species and latitude (David et al. 2015). Under laboratory conditions, out-of-season spawning of wild caught Spotted Gar can produce winter cohorts (Bodin 2018). ...
... Broodstock sex ratios of 1:3 and 1:4 (female:male) are recommended although different ratios, single pairs, and gamete stripping have resulted in successful spawns and embryo production (Boudreaux 2006;Márquez-Couturier et al. 2006;Amores et al. 2011;David et al. 2015;Porta et al. 2019). A variety of non-lethal, species-specific morphologic features and vitellogenin assays have been used to assign sex of individual broodstock (Love 2004;Mendoza et al. 2012;McDonald et al. 2013;McDonald et al. 2018). ...
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Growing appreciation of biodiversity and the role of apex predators, along with increasing popularity of multispecies and trophy‐oriented angling, has elevated the status of gars – in particular, the Alligator Gar Atractosteus spatula – among anglers and biologists alike. As a result, considerable effort has been spent in recent years to gain a working knowledge of the biology and ecology of the species in order to advance science‐based management. In January 2019, the Southern Division of the American Fisheries Society Alligator Gar Technical Committee hosted a symposium entitled, Advances in the conservation and management of North American gars to showcase the results of research and management efforts conducted throughout the species’ range. Fishery researchers and managers presented a diversity of works, furthering our understanding of population dynamics, stock assessment, genetics, hatchery practices and stocking, habitat use, and angler desires associated with Alligator Gar fisheries. In this introduction to our special section, we introduce these works and provide a synthesis of the current state of scientific knowledge regarding the Alligator Gar. We hope that this will provide context to the works presented in the symposium, and serve to guide the development of future research that addresses remaining knowledge gaps concerning the species and its growing fishery.
... Future studies should also explore growth of age-0 alligator gar from northern populations, as growth may be slower as a result of cooler temperatures and a shorter growing season. Alternatively, age-0 alligator gar from Midwestern populations may grow even more rapidly than their southern counterparts as an adaptive response to compensate for a shorter growing season at higher latitudes (i.e., countergradient variation in growth; Conover & Present, 1990;David, Kik, Diana, Rutherford, & Wiley, 2015). The potential for countergradient variation in growth has been documented in spotted gar (David et al., 2015). ...
... Alternatively, age-0 alligator gar from Midwestern populations may grow even more rapidly than their southern counterparts as an adaptive response to compensate for a shorter growing season at higher latitudes (i.e., countergradient variation in growth; Conover & Present, 1990;David, Kik, Diana, Rutherford, & Wiley, 2015). The potential for countergradient variation in growth has been documented in spotted gar (David et al., 2015). Future research should more directly investigate the potential for latitudinal variation in growth by comparing the growth of age-0 alligator gar over a wider geographic range. ...
Article
We estimated the daily age and growth of wild age‐0 alligator gar (Atractosteus spatula) from Choke Canyon Reservoir and the Guadalupe and Trinity rivers, Texas, USA. Growth rates of wild age‐0 alligator gar were compared across systems, as well as to alligator gar reared in a Texas hatchery. Estimated ages of alligator gar ranged from 7 to 80 days in Choke Canyon Reservoir (n = 140), 11–73 days in the Guadalupe River (n = 16), and 4–115 days in the Trinity River samples (n = 245). Alligator gar growth was faster in the Trinity and Guadalupe rivers than growth in Choke Canyon Reservoir. Growth of alligator gar in Choke Canyon Reservoir (3.60 ± 0.08 mm/day), the Guadalupe River (4.76 ± 0.35 mm/day), and the Trinity River (5.13 ± 0.07 mm/day) was faster than growth of hatchery reared fish (3.41 ± 0.08 mm/day). This study represents the first account of early growth of age‐0 alligator gar in the wild, and documents some of the fastest growth of age‐0 fish among freshwater fishes. We attribute the rapid growth of wild alligator gar to their quick transition to piscivory at early stages, and their effective use of habitat and resources on inundated floodplains during flood pulses. Future studies should explore the effects of environmental factors on the hatching success, growth, and survival of age‐0 alligator gar.
... Studies conducted since the widespread use of daily aging in the 1980s suggest a latitudinal trend in snook growth (mm SL d −1 ): 0.44 (Puerto Rico, Aliaume et al. 2000), 0.49 (conducted during a period of mild winters in Tampa Bay, Florida, Schulz et al., 2020), 0.6-0.7 (conducted during a period of cold winters in Tampa Bay, Florida, McMichael et al. 1989), and 0.72 (North Inlet-Winyah Bay estuarine system, South Carolina, present study). Faster fish growth in colder climates that have shorter growing seasons has been well established (Conover 1990;Solomon et al. 2015). Genetic adaptation can allow for rapid changes in life history traits, particularly for species that are expanding their range. ...
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Given recent trends of warming water temperatures and shifting fish distributions, detecting range expansion is important for resource management and planning. The subtropical common snook Centropomus undecimalis (hereafter referred to as snook) is an estuarine species that historically extended from the tropics to southern portions of Florida and Texas, but this range has been expanding for the past decade. We collected juvenile snook (n = 16; size range = 96–210-mm standard length [SL]) in saltmarshes of South Carolina, which is well outside their usual range but not unprecedented. Growth rates of juvenile snook in South Carolina (0.72-mm SL d−1) were similar to those reported for Florida during a cold period, but faster than rates reported for Florida during a recent period of mild winters (0.49-mm SL d−1). Based on collection and estimated hatch dates, and supported by winter water temperature records, juvenile snook overwintered for at least 1 year allowing them to grow to sizes that are typical for emigration from nursery habitats to open estuarine shorelines. Continued work is needed to determine whether there is potential for ongoing range expansion of snook to the region, and a strategy is proposed to focus on future research.
... The McMichael et al. (1989) collections occurred during the mid-1980s when consecutive winters were severe enough to constrict the distributions of tropical species like mangroves (Stevens et al. 2006). Thus, it follows that juvenile snook growth could have been stunted during cold winters of the mid-1980s with fast compensatory growth occurring during summers, a phenomenon that is well documented in other fishes (Conover 1990;Solomon et al. 2015). Differences in growth between cool and warm months were less apparent during the current study, which took place during a period of mild winters. ...
Article
Increasing human populations and urban development have led to losses of estuarine habitats for fish and wildlife. Where resource managers are restoring coastal wetlands, in addition to meeting goals related to hydrologic connectivity, biodiversity, and recreational opportunities, efforts are being made to provide habitat that is suitable for juvenile sportfish. An 18‐month study was conducted to compare juvenile sportfish use of natural, restored, and impacted sites along Tampa Bay, Florida shorelines. Juvenile sportfish densities were broadly comparable to natural sites and greater than impacted sites. However, site‐specific differences in sportfish use did occur within site types. For example, one restored site had significantly higher densities of red drum Sciaenops ocellatus than any other site, while black drum Pogonias cromis were found exclusively at another restored site. To evaluate whether the restored sites are providing suitable habitat for juvenile fish, we assessed growth (estimated from counts of daily rings on otoliths) and condition (determined by lipid analyses) of juvenile common snook Centropomus undecimalis , an archetypal coastal wetland‐dependent species. Growth (0.43–0.56 mm/day) and condition (4.6–6.1% lipid of dry weight) exhibited only site‐specific differences and did not vary among natural, restored, and impacted site types. Although mortality rates of juvenile sportfish were not determined, use of a 40‐m seine found that densities of potential piscine predators in these coastal wetlands were relatively low compared to published studies of open estuarine shorelines. The restoration and creation of coastal wetlands in Tampa Bay provides improved habitat for juvenile sportfish. This article is protected by copyright. All rights reserved.
... The Alligator Gar, for example, has a southerly distribution in North America (from~21°N to 39°N; Grande 2010; Smith et al., in press [this special section]) and has been extirpated from most of its historic northern range (David et al. 2018). The Spotted Gar is a more northerly species (from~28°N to 44°N; Grande 2010) that is considered a species of conservation concern at the northern edge of its range and critically imperiled in Canada (Glass et al. 2011;Staton et al. 2012;David et al. 2015;OMNRF 2016). Although habitat loss has largely been implicated in the declines of northern Spotted Gar populations (Glass et al. 2011), temperature at the northern extreme of the species' range could also affect spawning, hatching, and larval development (Ficke et al. 2007). ...
Article
Water temperature influences both morphological and physiological development in fishes. However, the effects of water temperature on the early development of Alligator Gar Atractosteus spatula and Spotted Gar Lepisosteus oculatus are not well understood. Both gar species were collected from natural environments and spawned in a hatchery setting. After spawning, fertilized embryos were collected and transferred to the Oklahoma Fishery Research Laboratory, where the embryos (50–72 embryos/treatment) were placed into one of five water temperature treatments (15.5, 20.0, 23.8, 27.5, and 32.2°C) and observed over time to estimate the time to hatch and the time to reach the free‐swimming stage. Both species showed an inverse relationship between temperature and the timing of hatch and advancement to free‐swimming fingerlings for all treatments. In addition, Alligator Gar embryos did not develop at the coldest water temperature tested, and Alligator Gar juveniles held at the warmest temperature tested were observed with developmental abnormalities, potentially affecting their survival. The same temperature extremes had no comparable negative effect on Spotted Gar. The results of this study are useful for understanding early life history dynamics of these two species in their natural environments and can also be used by hatchery managers who are seeking to optimize their production protocols.
... Although many species are globally secure, populations of some are threatened or imperiled, such as the Spotted Gar Lepisosteus oculatus in Canada (OMNRF 2016) and in certain states within the USA (Kansas, Ohio, Pennsylvania, Georgia, and Illinois; Staton et al. 2012;NatureServe 2018). Early life history of Spotted Gars remains poorly understood, with studies mainly focusing on adults (Love 2004;Bonvillain et al. 2008;Glass et al. 2011;Staton et al. 2012;David et al. 2015). For many fishes, the early life stages are critical for population maintenance (Chambers and Trippel 1997), but information on these stages is often scarce. ...
Article
Gars (Lepisosteidae) are increasingly being managed as top‐level predators important to overall ecosystem health. There is a paucity of information on early life history for many species, which would aid their conservation and management. Daily rings in otoliths are useful for determining many early life‐history parameters, such as growth rates and date of hatch, but properly interpreting these structures requires additional information on otolith formation. Gars represent an ancient lineage and their otoliths are unlike those of most teleost fishes, having multiple nuclei and covered on the surface with very small otoconia. We used computed tomography (CT) X‐ray scanning and oxytetracycline (OTC) marking of a series of known‐age fish from hatch through 10‐12 days post‐hatch (dph) to understand the formation of otoliths in Spotted Gar Lepisosteus oculatus, a species that is of management concern in several parts of its range in North America. The sagittae and lapilli each began as loose associations of otoconia at hatch, and fused and hardened into single crystals by 4 dph, in concert with the transition from attached larvae to free‐swimming juvenile. Asterisci otoliths were not observed in any of the individuals examined through 12 dph. Oxytetracycline marks were not observed on individuals treated at hatch and variable marks were detected at 1 dph through 5 dph. By 6 dph, 100% of individuals exhibited OTC marks on sagittae and lapilli. Daily rings could not be discerned until fish were marked 4 dph, after which, daily age estimates increased linearly with fish age. Results of this study verify that otoliths (sagittae and lapilli) of Spotted Gar and their daily rings form several days after hatch, in relation to the transition from sessile, attached larvae to free‐swimming juvenile. This article is protected by copyright. All rights reserved.
... Knowledge of the basic biology and life history of holostean species is limited, however (Binion et al. 2015;David et al. 2015;Smylie et al. 2015). Information on the vital rates (growth, mortality, and dispersal) of holostean populations lags far behind that for most other fisheries, and little is known about the behavior and habitats of juvenile holosteans (Solomon et al. 2013). ...
... Among the Lepisosteus species, the Florida, Shortnose, and Longnose gars have stable populations and are not considered to be at risk (NatureServe 2013). However, peripheral populations of Spotted Gars in Ontario and the Great Lakes states are of special concern and conservation interest (Ohio Department of Natural Resources 2012; Committee on the Status of Endangered Wildlife in Canada 2015; David et al. 2015). ...
Article
Gars (family Lepisosteidae) play important roles as apex predators in freshwater ecosystems, helping to balance fish populations. Several gar species are exploited as food and game fish, and some species are classified as vulnerable due to habitat loss. New molecular techniques to detect, monitor, and identify environmental DNA from gars might help inform management and conservation efforts for these interesting fish. The goal of this project was to develop and test PCR primers for gars, using specimens of all seven gar species, which are on exhibit at the Belle Isle Aquarium in Detroit, Michigan. Focusing on the mitochondrial gene for cytochrome oxidase I, we first designed primers to amplify DNA from all species of gars (“universal gar primers”) and confirmed their specificity in silico. These primers amplified DNA from all seven species, and species identities were confirmed by sequencing the PCR products. Only one of the three ostensibly Shortnose Gar Lepisosteus platostomus specimens sampled exhibited a Shortnose Gar matriline; two other specimens may be Longnose Gar L. osseus × Shortnose Gar hybrids. Genus‐targeted primers were developed that amplified all Atractosteus species and two of four Lepisosteus species. Species‐specific primers were developed for Longnose Gar, Shortnose Gar, and Tropical Gar Atractosteus tropicus. A primer set that targeted Alligator Gar A. spatula also amplified DNA from Cuban Gar A. tristocheus, but not other species. While the universal gar primers followed by sequencing confirmed the identities of all seven gar species at the Belle Isle Aquarium, PCR with the species‐specific primers enabled direct detection of the presence of DNA from the targeted species in the water in which those species had been maintained. Designing these primers is the first step in developing eDNA markers for gars, which in turn could inform the conservation and management of gar populations. This article is protected by copyright. All rights reserved.
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We used life-history theory to predict reaction norms for age and size at maturation. We assumed that fecundity increases with size and that juvenile mortality rates of offspring decrease as ages-at-maturity of parents increase, then calculated the reaction norm by varying growth rate and calculating an optimal age at maturity for each growth rate. The reaction norm for maturation should take one of at least four shapes that depend on specific relations between changes in growth rates and changes in adult mortality rates, juvenile mortality rates, or both. Most organisms should mature neither at a fixed size nor at a fixed age, but along an age-size trajectory. The model makes possible a clear distinction between the genetic and phenotypic components of variation. The evolved response to selection is reflected in the shape and position of the reaction norm. The phenotypic response of a single organism to rapid or slow growth is defined by the location of its maturation event as a point on the reaction norm. A quantitative test with data from 19 populations and species of fish showed that predictions were in good agreement with observations (r = 0.93, P < 0.0001). The predictions of the model also agreed qualitatively with observed phenotypic variation in age and size at maturity in humans, platyfish, fruit flies, and red deer. This preliminary success suggests that experiments designed to test the predictions directly will be worthwhile.
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I studied the ecology and biogeography of the Spotted Gar (Lepisosteus oculatus) from core and Great Lakes Region peripheral populations. Peripheral populations occupy the edge of a species’ range and are considered to be important in terms of a species’ ecology, biogeography, evolution, and conservation. Peripheral populations often persist under different environmental conditions from the species’ core populations, and may exhibit adaptations to potentially “harsher” marginal environments. In this study I used common garden experiments, life history analyses, and phylogeography (based on mitochondrial DNA) to address the overall hypothesis that spotted gars from peripheral, Great Lakes Basin populations exhibit distinct life history characteristics and patterns of genetic diversity in comparison to Spotted Gars from core populations. In common garden laboratory experiments young-of-year Spotted Gars from peripheral populations exhibited significantly faster growth rates (0.09 cm/day, 0.26 g/day) than core populations (0.04 cm/day, 0.11 g/day, suggesting countergradient variation in growth. Life history analysis based on length-at-age data from 5 field populations (2 peripheral, 3 core) and incorporating thermal opportunity for growth (degree days above 18 °C) indicated significantly higher growth rate in Spotted Gars from peripheral (1.23 mm/degree day) compared to core populations (0.22 mm/degree day). Catch-curve analyses of the same populations indicated annual mortality rate (A) was lower in peripheral (A = 0.41) compared to core populations (0.56). Analysis of mitochondrial DNA from core and peripheral populations indicated genetic diversity (haplotype diversity, H) was highest in the Mississippi River Basin (H = 0.80), lowest in the Great Lakes Basin (H = 0.00, single haplotype), and most divergent in the western Gulf Coast Basin (H = 0.70, no haplotypes shared with other basins). Overall, the Great Lakes Basin population was shown to be a unique component of the species, and is adapted to life at higher latitudes with shorter growing seasons. As a useful case study, my work can inform gar conservation strategies and lead to a better general understanding of the evolution and maintenance of vertebrate life history patterns and genetic diversity.
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Wolverines are highly vagile carnivores, with long-distance dispersal documented for males and females. Consequently, the species was thought to represent 1 large, panmictic unit in North America. In this study, we examined the connectivity of populations on the edge of their historical distribution to the larger, continuous, northern distribution of wolverines. Twenty-two regions were sampled, and 671 individuals were genotyped at 12 microsatellite loci. Our results confirmed that high levels of gene flow do occur among all the northern wolverine populations sampled. We also observed progressively increasing genetic structure at the periphery of their southern and eastern distributions, suggesting that these populations may have been partially fragmented from what was once a panmictic unit. Peripheral populations may be more susceptible to extirpation and, therefore, may be the most appropriate targets for concerted conservation efforts to prevent the elimination of wolverines from yet more of their historical range.
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Intrinsic growth rate is emerging as an important life-history trait that can be modified by natural selection. One factor determining optimal intrinsic growth rates is the pattern of resource availability. Organisms that experience chronically low resource levels tend to have slow intrinsic growth rates. However, this does not necessarily hold if resource levels change as an organism grows. We present a theoretical model showing that rapid growth is favored when resource levels for small size classes are low relative to resource levels for large size classes. We call such a growth strategy "optimistic" because rapid growth is based on an expectation that resources will improve once a minimum size is reached. We provide empirical support for this hypothesis by examining the intrinsic growth rates of pumpkinseed sunfish derived from three populations sympatric with bluegill sunfish (an important competitor with small size classes) to three populations allopatric with bluegill sunfish raised under common conditions. Rapid growth has evolved in the sympatric fish to reach the size refuge from competition as quickly as possible.
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Understanding the spatial context of genetic variation for species at risk is important for effective management and long-term survival of the species. We use multilocus microsatellite data to investigate the population genetic structure of the spotted gar (Lepisosteus oculatus) across its northern range edge in Canada. We then compare these northern individuals with samples taken from the southern core of the species range. For the northern samples , significant genetic differentiation among groups of individuals forming two major genetically distinct populations, and as many as 7–9 smaller subpopulations, was recovered using hierarchical Bayesian assignment methods and non-equilibrial discriminant function analyses. Spatial genetic variation is present, particularly at higher hierarchical groupings; however, some population admixture at sites is evident and is indicative of dispersal and gene flow among some locations or shared ancestry. Gene flow estimates among populations and subpopula-tions is very low, ranging from essentially complete isolation to as high as 5 %—suggesting that mechanisms in addition to geographic isolation are operating to create genetic structure. In Lake Erie, the physical isolation of Point Pelee appears to confer distinct genetic differentiation for those populations and provide a source of genetic variation for Lake Erie proper when breaches to the barrier beach occur. Results indicate that the northern edge populations are distinct from southern populations and should be conserved to maintain the overall genetic diversity of this species. Additionally, the asymmetrical genetic connectivity among the Point Pelee and Rondeau Bay sites highlights the sensitivity of Point Pelee to environmental perturbation and habitat degradation.
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Back in print! This magnificent, encyclopedic reference to 157 fish species which are found not only in Wisconsin but also in much of the Great Lakes region and Mississippi River watershed has been a model for all other such works. In addition to comprehensive species accounts, Becker discusses water resources and fisheries management from both historical and practical policy perspectives."
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Introduction to the Zoogeography of North American Fishes Ichthyofaunal Patterns on a Geographic Grid Zoogeography on Freshwater Fishes of the Hudson Bay Drainage, Ungava Bay, and the Arctic Archipelago The Fish Fauna of the Laurentian Great Lakes, the St Lawrence Lowlands, Newfoundland and Labrador Zoogeography of the Northern Appalachians Zoogeography of the Fishes of the Central Appalachians and the Central Atlantic Coastal Plain Zoogeography of the Freshwater Fishes of the Southeastern United States' Savannah River to Lake Ponchartrain Zoogeographic Implications of the Mississippi River Basin Zoogeography of Fishes of the Lower Ohio-Upper Mississippi Basin Drainage Evolution and Fish Biogeography of the Tennessee and Cumberland Rivers Drainage Relm Fishes in the Western Mississippi Drainage Zoogeography of Freshwater Fishes of the Western Gulf Slope The Evolution of the Rio Grande Basin as Inferred from Its Fish Fauna Origin and Geography of the Fishes of Central Mexico Geography of Western North America Freshwater Fishes' Description and Relationships to Intracontinental Tectonism Zoogeography of the Freshwater of Cascadia (The Columbia System and Rivers North to the Stikine) Zoogeography of Fishes of the Yukon and Mackenzie Basins Distribution of Exotic Fishes in North America Review of the Fossil History of North America Freshwater Fishes Literature Cited Index.