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Size-frequency distributions along a latitudinal gradient in Middle Permian fusulinoideans.

Zhang Y, Payne JL - PLoS ONE (2012)

Bottom Line: We recovered the following results: keriothecal fusulinoideans are substantially larger than nonkeriothecal fusulinoideans; fusulinoideans from the equatorial zone are typically larger than those from the north and south transitional zones; neoschwagerinid specimens within a single species are generally larger in the equatorial zone than those in both transitional zones; and the nonkeriothecal fusulinoideans Staffellidae and Schubertellidae have smaller size in the north transitional zone.Temporal variation in atmospheric oxygen concentrations have been shown to account for temporal variation in fusulinoidean size during Carboniferous and Permian time, but oxygen availability appears unlikely to explain biogeographic variation in fusulinoidean sizes, because dissolved oxygen concentrations in seawater typically increase away from the equator due to declining seawater temperatures.Consequently, our findings highlight the fact that spatial gradients in organism size are not always controlled by the same factors that govern temporal trends within the same clade.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, CAS, Nanjing, Jiangsu, China. geozyc@yahoo.com

ABSTRACT
Geographic gradients in body size within and among living species are commonly used to identify controls on the long-term evolution of organism size. However, the persistence of these gradients over evolutionary time remains largely unknown because ancient biogeographic variation in organism size is poorly documented. Middle Permian fusulinoidean foraminifera are ideal for investigating the temporal persistence of geographic gradients in organism size because they were diverse and abundant along a broad range of paleo-latitudes during this interval (~275-260 million years ago). In this study, we determined the sizes of Middle Permian fusulinoidean fossils from three different paleo-latitudinal zones in order to examine the relationship between the size of foraminifers and regional environment. We recovered the following results: keriothecal fusulinoideans are substantially larger than nonkeriothecal fusulinoideans; fusulinoideans from the equatorial zone are typically larger than those from the north and south transitional zones; neoschwagerinid specimens within a single species are generally larger in the equatorial zone than those in both transitional zones; and the nonkeriothecal fusulinoideans Staffellidae and Schubertellidae have smaller size in the north transitional zone. Fusulinoidean foraminifers differ from most other marine taxa in exhibiting larger sizes closer to the equator, contrary to Bergmann's rule. Meridional variation in seasonality, water temperature, nutrient availability, and carbonate saturation level are all likely to have favored or enabled larger sizes in equatorial regions. Temporal variation in atmospheric oxygen concentrations have been shown to account for temporal variation in fusulinoidean size during Carboniferous and Permian time, but oxygen availability appears unlikely to explain biogeographic variation in fusulinoidean sizes, because dissolved oxygen concentrations in seawater typically increase away from the equator due to declining seawater temperatures. Consequently, our findings highlight the fact that spatial gradients in organism size are not always controlled by the same factors that govern temporal trends within the same clade.

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Size distributions of species endemic to indicated regions, using the largest specimen for each species in each region.(A) All species. (B) Ozawainellidae. (C) Staffellidae. (D) Schubertellidae. (E) Schwagerinidae. (F) Neoschwagerinidae. (G) Verbeekinidae. Boxes and whiskers as in Figure 2. * p<0.05; ** p<0.01; *** p<0.001. Significance levels of all comparisons are presented in Table 3.
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pone-0038603-g005: Size distributions of species endemic to indicated regions, using the largest specimen for each species in each region.(A) All species. (B) Ozawainellidae. (C) Staffellidae. (D) Schubertellidae. (E) Schwagerinidae. (F) Neoschwagerinidae. (G) Verbeekinidae. Boxes and whiskers as in Figure 2. * p<0.05; ** p<0.01; *** p<0.001. Significance levels of all comparisons are presented in Table 3.

Mentions: There is substantial evidence for variation in the overall size distribution of fusulinoidean species as a function of latitude (Fig. 3A). The mean values of size distribution for equatorial fusulinoidean species are significantly larger than those for the north and south transitional zones (Mann Whitney U-test: equatorial versus north transitional zone, two-tailed p = 0.0002; equatorial versus south transitional zone, two-tailed p = 0.007; see also Table 1). A bootstrap resampling analysis (10,000 replicates) of species from the equatorial region shows that the differences in maximum size between the equatorial region and transitional zones are also larger than can be explained simply by differences in diversity (bootstrap resampling using 10,000 replicates: equatorial versus south, p = 0.007; equatorial versus north, p = 0.10) but the second-largest species from the north is substantially smaller (2.89 versus 2.59 log mm3). Median sizes across species are statistically indistinguishable between the north and south transitional zones (Mann Whitney U-test: p = 0.22). These size differences result from both within- and among-species differences in size. The largest equatorial representative of a species is on average significantly larger than the largest conspecific specimen from either transitional zone (Fig. 4A; two-tailed t-test: equatorial versus north transitional zone, p<0.0001; equatorial versus south transitional zone, p<0.0001), whereas there is no tendency for the largest representative of a given species from the north transitional zone to be either larger or smaller than the largest conspecific specimen from the south transitional zone (Fig. 4A; two-tailed t-test: p = 0.43). Species endemic to the equatorial zone are also larger, on average, than species endemic to either transitional zone (Fig. 5A; two-tailed Mann-Whitney test: equatorial versus north transitional zone, p = 0.002; equatorial versus south transitional zone, p = 0.006) whereas the median sizes of endemics from the two transitional zones are statistically indistinguishable from one another (two-tailed Mann-Whitney test: p = 0.83).


Size-frequency distributions along a latitudinal gradient in Middle Permian fusulinoideans.

Zhang Y, Payne JL - PLoS ONE (2012)

Size distributions of species endemic to indicated regions, using the largest specimen for each species in each region.(A) All species. (B) Ozawainellidae. (C) Staffellidae. (D) Schubertellidae. (E) Schwagerinidae. (F) Neoschwagerinidae. (G) Verbeekinidae. Boxes and whiskers as in Figure 2. * p<0.05; ** p<0.01; *** p<0.001. Significance levels of all comparisons are presented in Table 3.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3369838&req=5

pone-0038603-g005: Size distributions of species endemic to indicated regions, using the largest specimen for each species in each region.(A) All species. (B) Ozawainellidae. (C) Staffellidae. (D) Schubertellidae. (E) Schwagerinidae. (F) Neoschwagerinidae. (G) Verbeekinidae. Boxes and whiskers as in Figure 2. * p<0.05; ** p<0.01; *** p<0.001. Significance levels of all comparisons are presented in Table 3.
Mentions: There is substantial evidence for variation in the overall size distribution of fusulinoidean species as a function of latitude (Fig. 3A). The mean values of size distribution for equatorial fusulinoidean species are significantly larger than those for the north and south transitional zones (Mann Whitney U-test: equatorial versus north transitional zone, two-tailed p = 0.0002; equatorial versus south transitional zone, two-tailed p = 0.007; see also Table 1). A bootstrap resampling analysis (10,000 replicates) of species from the equatorial region shows that the differences in maximum size between the equatorial region and transitional zones are also larger than can be explained simply by differences in diversity (bootstrap resampling using 10,000 replicates: equatorial versus south, p = 0.007; equatorial versus north, p = 0.10) but the second-largest species from the north is substantially smaller (2.89 versus 2.59 log mm3). Median sizes across species are statistically indistinguishable between the north and south transitional zones (Mann Whitney U-test: p = 0.22). These size differences result from both within- and among-species differences in size. The largest equatorial representative of a species is on average significantly larger than the largest conspecific specimen from either transitional zone (Fig. 4A; two-tailed t-test: equatorial versus north transitional zone, p<0.0001; equatorial versus south transitional zone, p<0.0001), whereas there is no tendency for the largest representative of a given species from the north transitional zone to be either larger or smaller than the largest conspecific specimen from the south transitional zone (Fig. 4A; two-tailed t-test: p = 0.43). Species endemic to the equatorial zone are also larger, on average, than species endemic to either transitional zone (Fig. 5A; two-tailed Mann-Whitney test: equatorial versus north transitional zone, p = 0.002; equatorial versus south transitional zone, p = 0.006) whereas the median sizes of endemics from the two transitional zones are statistically indistinguishable from one another (two-tailed Mann-Whitney test: p = 0.83).

Bottom Line: We recovered the following results: keriothecal fusulinoideans are substantially larger than nonkeriothecal fusulinoideans; fusulinoideans from the equatorial zone are typically larger than those from the north and south transitional zones; neoschwagerinid specimens within a single species are generally larger in the equatorial zone than those in both transitional zones; and the nonkeriothecal fusulinoideans Staffellidae and Schubertellidae have smaller size in the north transitional zone.Temporal variation in atmospheric oxygen concentrations have been shown to account for temporal variation in fusulinoidean size during Carboniferous and Permian time, but oxygen availability appears unlikely to explain biogeographic variation in fusulinoidean sizes, because dissolved oxygen concentrations in seawater typically increase away from the equator due to declining seawater temperatures.Consequently, our findings highlight the fact that spatial gradients in organism size are not always controlled by the same factors that govern temporal trends within the same clade.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, CAS, Nanjing, Jiangsu, China. geozyc@yahoo.com

ABSTRACT
Geographic gradients in body size within and among living species are commonly used to identify controls on the long-term evolution of organism size. However, the persistence of these gradients over evolutionary time remains largely unknown because ancient biogeographic variation in organism size is poorly documented. Middle Permian fusulinoidean foraminifera are ideal for investigating the temporal persistence of geographic gradients in organism size because they were diverse and abundant along a broad range of paleo-latitudes during this interval (~275-260 million years ago). In this study, we determined the sizes of Middle Permian fusulinoidean fossils from three different paleo-latitudinal zones in order to examine the relationship between the size of foraminifers and regional environment. We recovered the following results: keriothecal fusulinoideans are substantially larger than nonkeriothecal fusulinoideans; fusulinoideans from the equatorial zone are typically larger than those from the north and south transitional zones; neoschwagerinid specimens within a single species are generally larger in the equatorial zone than those in both transitional zones; and the nonkeriothecal fusulinoideans Staffellidae and Schubertellidae have smaller size in the north transitional zone. Fusulinoidean foraminifers differ from most other marine taxa in exhibiting larger sizes closer to the equator, contrary to Bergmann's rule. Meridional variation in seasonality, water temperature, nutrient availability, and carbonate saturation level are all likely to have favored or enabled larger sizes in equatorial regions. Temporal variation in atmospheric oxygen concentrations have been shown to account for temporal variation in fusulinoidean size during Carboniferous and Permian time, but oxygen availability appears unlikely to explain biogeographic variation in fusulinoidean sizes, because dissolved oxygen concentrations in seawater typically increase away from the equator due to declining seawater temperatures. Consequently, our findings highlight the fact that spatial gradients in organism size are not always controlled by the same factors that govern temporal trends within the same clade.

Show MeSH