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The paradox of gradualism: phyletic evolution in two lineages of lymnocardiid bivalves (Lake Pannon, central Europe)
- Dana H. Geary, Gene Hunt, Imre Magyar, Holly Schreiber
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- Journal:
- Paleobiology / Volume 36 / Issue 4 / Fall 2010
- Published online by Cambridge University Press:
- 08 April 2016, pp. 592-614
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Patterns preserved in the fossil record are of the highest importance in addressing questions about long-term evolutionary processes, yet both the description of pattern and its translation into process can be difficult. With respect to gradual phyletic change, we know that randomly generated sequences may exhibit characteristics of a “trend” apparent patterns, therefore, must be interpreted with caution. Furthermore, even when the claim of a gradual trend can be statistically justified, interpretation of the underlying mechanisms may be challenging. Given that we can observe populations changing rapidly over tens or hundreds of years, it is now more difficult to explain instances of geologically gradual (as opposed to punctuated) change.
Here we describe morphologic change in two bivalve lineages from the late Miocene Lake Pannon. We evaluate change according to the model-based methods of Hunt. Both lineages exhibit size increases and shape changes over an interval of nearly 4 million years. Size and two shape variables in the conjungens lineage are best fit by a model of directional evolution; remaining shape variables mostly conform to unbiased random walks. Body-size evolution in the diprosopum lineage is also significantly directional but all shape variables are best fit by the unbiased random walk model; the small number of sampling intervals available for this lineage (n = 6) makes determination of the actual pattern more difficult. Model-fitting results indicate that the parallel trajectories of increasing log shell height over time in the two lineages can be accounted for by an underlying trend shared by both lineages, suggesting that the size increases may be a shared response to the same cause. The pace of phenotypic change, measured as Lynch's Δ, is slower than the neutral expectation for all size and shape traits.
Our examples illustrate well the paradox of gradualism; the sequences exhibit significant directional morphological evolution, but rates of change as measured over the long-term are apparently too slow for directional selection or even drift to be the cause. Viewing long-term phenotypic evolution in terms of populations tracking peaks on adaptive landscapes is useful in this context. Such a view allows for intervals of directional selection (during times of peak movement–resulting in the overall trends we can detect) interspersed with intervals of stasis (during times of peak stability–resulting in overall changes that appear to proceed more slowly than the neutral expectation). The paradox of gradualism thus reduces to (1) peak movements and their drivers, which are not restricted in rate as are population-genetic drivers, and (2) the maintenance of stasis, on which no consensus exists.
We can identify no environmental parameter in the central European Neogene that exhibits consistent change across the interval of gradual morphologic change. It may be that in Lake Pannon the long-term persistence of generally ameliorating conditions (plentiful resources and habitat space, few predators or competitors) resulted in geologically slow but consistent peak shifts, which in turn facilitated size increase and shape change in these lineages.
Assessing foods offered in the Food Distribution Program on Indian Reservations (FDPIR) using the Healthy Eating Index 2010
- Carmen Byker Shanks, Teresa Smith, Selena Ahmed, Holly Hunts
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- Journal:
- Public Health Nutrition / Volume 19 / Issue 7 / May 2016
- Published online by Cambridge University Press:
- 24 September 2015, pp. 1315-1326
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Objective
To assess the nutritional quality of food packages offered in the Food Distribution Program on Indian Reservations (FDPIR) using the Healthy Eating Index 2010 (HEI-2010).
DesignData were collected from the list of the food products provided by the US Department of Agriculture’s Food and Nutrition Handbook 501 for FDPIR. Nutritional quality was measured through a cross-sectional analysis of five randomly selected food packages offered through FDPIR. HEI-2010 component and total scores were calculated for each food package. ANOVA and t tests assessed significant differences between food packages and HEI-2010 maximum scores, respectively.
SettingThis study took place in the USA.
SubjectsStudy units included food products offered through FDPIR.
ResultsThe mean total HEI-2010 score for the combined FDPIR food packages was significantly lower than the total HEI-2010 maximum score of 100 (66·38 (sd 11·60); P<0·01). Mean scores for total fruit (3·52 (sd 0·73); P<0·05), total vegetables (2·58 (sd 0·15); P<0·001), greens and beans (0·92 (sd 1·00); P<0·001), dairy (5·12 (sd 0·63); P<0·001), total protein foods (4·14 (sd 0·56); P<0·05) and refined grains (3·04 (sd 2·90); P<0·001) were all significantly lower than the maximum values.
ConclusionsThe FDPIR food package HEI-2010 score was notably higher than other federal food assistance and nutrition programmes. Study findings highlight opportunities for the FDPIR to modify its offerings to best support lifestyles towards prevention of diet-related chronic disease.