*3.2. Effects of Vegetation Cover and Turtle Body Size*

Our GLM results (Table 2) showed a negative effect of vegetation cover on Anura adults' consumption by turtles, and showed that the frequencies of Anura tadpoles, fish, reptiles and birds on *Pelusios* diets increased with the increase in vegetation cover. The GLM model also showed positive effects of individual body size on algae, Bivalvia, reptiles, birds and small mammals' consumption by turtles, and underlined that the predation on Arachnida decreased with the increase in turtle body size (Table 3).

**Figure 8.** UPGMA, with Euclidean distances and 40 bootstraps as branching measurement, showing the dissimilarities among the main habitats of the various study areas where *Pelusios* populations were studied for determining their taxonomic composition of the diet. FOR = forest; FORDER = forest-derived; SAV = savannah. FOR 1–4 and FORDER 1–4 were from Nigeria; SAV1 from Benin, SAV 2–3 from Togo, SAV 4–6 from South Sudan and SAV7 from Zambia.

**Table 2.** Output of the General Linear Model (GLM) on the relationship between vegetation cover and diet in four species of *Pelusios* from tropical Africa. Only significant variables are presented in this table.


**Table 3.** Output of the GLM on the relationship between turtle body size and diet in four species of *Pelusios* from tropical Africa. Only significant variables are presented in this table.


### *3.3. Effects of Sex and Ontogenetic Changes in the Diet Composition*

The summary of the food data collected by country and by sex, for the various *Pelusios* species, are presented in the Online Supplemental Tables S1–S5. We did not uncover any significant intersexual difference in the frequency of occurrence of the various prey items within the various *Pelusios* populations and by country (Table 4).


**Table 4.** Summary of the statistical results on the intersexual differences in taxonomic dietary composition within *Pelusios* populations from the various countries of Africa that were analyzed for this review. χ**<sup>2</sup>** test is calculated on the frequencies of occurrence of each food type category by sex, within each population studied in a given country.

In terms of ontogenetic diet composition, the data for the various species are presented in the Online Supplementary Material Tables S6–S9). For these analyses, we pooled data from males and females because of no significant intersexual differences in prey composition (see Table 4 and text at above). Concerning *P. castaneus*, the contingency table analysis revealed that there were significant differences in the frequency of consumption of the various food types by turtle size category (Table 5), with small individuals consuming significantly more insects than the two other size categories, intermediate sized and large individuals more fish and adult anurans (Table S6). These two latter categories were similar in terms of taxonomic composition of the diet, but large individuals fed upon adult anurans more frequently than intermediate sized individuals (Table S6). In *P. niger*, there was also a statistically significant ontogenetic dietary change (Table 5), with adult anurans, birds and small mammals being preyed upon particularly by large sized individuals, fish by both large and intermediate sized individuals, and insects by small sized individuals (Table S7). Insects also dominated in the diet of small-sized *P. adansonii*, whereas insects and fish were the main prey category for the large sized individuals, and aquatic plants, insects and annelids in the diet of average sized individuals (Table S8). Overall, also in this species, the ontogenetic dietary divergence was statistically significant (Table 5). Conversely, there was no significant ontogenetic divergence in *P. nanus* (Table 5), with insects being the main food type for the two size categories considered in this study (Table S9).

**Table 5.** Summary of the statistical results on the ontogenetic body-size-related differences in the taxonomical dietary composition within *Pelusios* populations from the various countries of Africa that were analyzed for this review. χ**<sup>2</sup>** test is calculated on the frequencies of occurrence of each food type category by turtle size category, within each population studied.


Our comparative data showed therefore that, whereas intersexual dietary divergence is virtually non-existent among *Pelusios* populations, there were instead significant ontogenetic diet variations in three out of four species. Both patterns are likely linked to the fact that intersexual dietary divergence should be expected in species with remarkable sexual size dimorphism [19] or in species with "telescopic growth" from newborn to adult age [14,20,21], whereas in our studied *Pelusios* species (apart from *P. niger* with males being much larger than females) the two sexes were relatively similar in size. In this regard, it is also interesting to mention that, consistent with theory [19–21], the species with the smallest absolute body size (*P. nanus*) did not show any ontogenetic dietary shifts.

We can therefore hypothesize that, in Pleurodira species, the diet composition (1) should be similar between males and females in those species exhibiting a minor sexual size dimorphism but not in those where one sex may reach much larger size than the other, and

(2) should be more ontogenetically variable in those species reaching larger adult sizes but still with small sized hatchlings. For instance, we expect a significant sexual size dimorphism in species such as *Pelusios sinuatus*, where the males may reach 35 cm and the females 55 cm carapace length and the size divergence between hatchlings and adults is remarkable [8,22,23].

#### **4. Conclusions**

In conclusion, our study revealed that all species of *Pelusios* analyzed here were substantially generalist in terms of their diet composition, although the effects of season (wet versus dry) and of other co-variates that are usually informative for field studies of turtles, including microhabitat characteristics and proximate meteorological conditions, were not assessed by our study. In addition, we showed that all species were omnivorous but with a clear preponderance of the prey items being of animal origin (amphibians, fish, arthropods and annelids), thus confirming earlier anecdotal accounts [8,10] and accounts from captivity (e.g., see <https://www.encyclo-fish.com/EN/paludarium/animals/pelusioscastaneus.php> (accessed on 10 April 2021). The relative head size and shape probably influenced the ingestion performance of the various species [24–27] and may possibly produce mechanisms of intraspecific niche partitioning [24,25]: indeed, when considering only the prey items that were found almost intact in the flushed stomachs, the species with the most massive head (*P. niger*) at a given body size was particularly able to ingest very large prey items compared to other species, and the larger-sized category of *P. niger* individuals also fed frequently upon larger size vertebrates, including even birds and small mammals. The ecological consequences (minimization of interspecific competition strength) of these differences in ingestion performance should be further analyzed by ad hoc studies.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10 .3390/d13040165/s1, Table S1: Diet composition (% of stomachs containing a given food item) of male and female *Pelusios* species in Nigeria, Table S2: Diet composition (% of stomachs containing a given food item) of male and female *Pelusios castaneus* in Benin, Table S3: Diet composition (% of stomachs containing a given food item) of male and female *Pelusios castaneus* in Togo, Table S4: Diet composition (% of stomachs containing a given food item) of male and female *Pelusios adansonii* in South Sudan, Table S5: Diet composition (% of stomachs containing a given food item) of male and female *Pelusios nanus* in Zambia, Table S6: Diet composition (% of stomachs containing a given food item) of the three body size categories of *Pelusios castaneus* (all countries being pooled), Table S7: Diet composition (% of stomachs containing a given food item) of the three body size categories of *Pelusios niger* (Nigeria), Table S8: Diet composition (% of stomachs containing a given food item) of the three body size categories of *Pelusios adansonii* (South Sudan), Table S9: Diet composition (% of stomachs containing a given food item) of the three body size categories of *Pelusios nanus* (Zambia).

**Author Contributions:** Conceptualization, L.L.; methodology, L.L.; formal analysis, L.L., M.D.V.; investigation, G.S.D., J.S.B., S.N.A., N.A.; resources, L.L.; data curation, F.P., D.D.; writing—original draft preparation, L.L.; writing—review and editing, all authors; supervision, L.L., G.C.A., E.A.E.; funding acquisition, L.L., F.P.; All authors have read and agreed to the published version of the manuscript.

**Funding:** Chelonian Research Foundation, Mohamed Bin Zayed Species Conservation Fund, Conservation International and Turtle Conservation Fund (to L.L. and F.P.).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data are presented in the paper and in the Online Supplemental Materials; additional data are available from authors on request.

**Acknowledgments:** We thank J. E. Fa, G.H. Segniagbeto, E, M. Hema, and S. Gonedele Bi, for helpful collaboration during the various research phases of this study. Two anonymous reviewers are thanked for their helpful comments on the submitted draft.

**Conflicts of Interest:** The authors declare no conflict of interest.
