Limited Dispersal and Significant Fine - Scale Genetic Structure in a Tropical Montane Parrot Species

<div><p>Tropical montane ecosystems are biodiversity hotspots harbouring many endemics that are confined to specific habitat types within narrow altitudinal ranges. While deforestation put these ecosystems under threat, we still lack knowledge about how heterogeneous environments like the montane tropics promote population connectivity and persistence. We investigated the fine-scale genetic structure of the two largest subpopulations of the endangered El Oro parakeet (<i>Pyrrhura orcesi</i>) endemic to the Ecuadorian Andes. Specifically, we assessed the genetic divergence between three sites separated by small geographic distances but characterized by a heterogeneous habitat structure. Although geographical distances between sites are small (3–17 km), we found genetic differentiation between all sites. Even though dispersal capacity is generally high in parrots, our findings indicate that dispersal is limited even on this small geographic scale. Individual genotype assignment revealed similar genetic divergence across a valley (~ 3 km distance) compared to a continuous mountain range (~ 13 km distance). Our findings suggest that geographic barriers promote genetic divergence even on small spatial scales in this endangered endemic species. These results may have important implications for many other threatened and endemic species, particularly given the upslope shift of species predicted from climate change.</p></div

Map of the global distribution range of El Oro parakeets and the study sites.

<p>(a) The global distribution range specified by the yellow area is based on recent population monitoring data of Cesar Garzon (marked elevational range: 800–1400 m). The dashed square specifies the study area. In the right-hand corner, the spatial location of the study area within Ecuador is shown. (b) Sampling locations at the southern (orange circles) and northern part (blue circles) of Buenaventura reserve and Cerro Azul (green circle). Dashed line in (b) specifies the borders of Buenaventura reserve. The Buenaventura valley separates BV_South and BV_North and lies outside the distribution range of parakeets (yellow area). Forested areas are highlighted in light green and inferred from geo-referenced satellite images (RapidEye, Blackbridge, Germany) taken in 2010 and 2013. Contour lines are given in 500 m steps.</p

Dispersal rates between the sampling locations inferred by BayesAss.

<p>Dispersal rates between the sampling locations inferred by BayesAss.</p

Significance levels for Wilcoxon test and Sign test for a recent bottleneck event measured as heterozygosity excess and assuming different mutation models.

<p>Significance levels for Wilcoxon test and Sign test for a recent bottleneck event measured as heterozygosity excess and assuming different mutation models.</p

Pairwise genetic differentiation measured as Jost´s D and G_ST and bias-corrected for small sample sizes (est).

<p>Pairwise genetic differentiation measured as Jost´s D and G_ST and bias-corrected for small sample sizes (est).</p

Genetic structure within the three study sites as inferred from the Structure analyses.

<p>Study sites comprise the southern area of Buenaventura (BV_South), the northern area of Buenaventura (BV_North) and Cerro Azul (CA). Each bar corresponds to an individual´s probability of belonging to a specific genetic cluster. Distinct clusters are assigned to different colours. Displayed are the results of Bayesian clustering analysis with prior information on sampling location for several numbers of K clusters. Presented are the results obtained a.) for the complete data set (n = 249) and b.) for the reduced data set (n = 65). The highest probability of clusters according to Evanno´s delta K was K = 2 for both data sets and K = 4 and K = 11 for the reduced and complete data set, respectively, using highest mean posterior likelihood.</p

Genetic diversity calculated as mean (± SE) for each sampling location and for the whole data set (N = sample size).

<p>Genetic diversity calculated as mean (± SE) for each sampling location and for the whole data set (N = sample size).</p

IL-7 treatment augments and prolongs sepsis-induced expansion of IL-10-producing B lymphocytes and myeloid-derived suppressor cells

<div><p>Immunological dysregulation in sepsis is associated with often lethal secondary infections. Loss of effector cells and an expansion of immunoregulatory cell populations both contribute to sepsis-induced immunosuppression. The extent and duration of this immunosuppression are unknown. Interleukin 7 (IL-7) is important for the maintenance of lymphocytes and can accelerate the reconstitution of effector lymphocytes in sepsis. How IL-7 influences immunosuppressive cell populations is unknown. We have used the mouse model of peritoneal contamination and infection (PCI) to investigate the expansion of immunoregulatory cells as long-term sequelae of sepsis with or without IL-7 treatment. We analysed the frequencies and numbers of regulatory T cells (Tregs), double negative T cells, IL-10 producing B cells and myeloid-derived suppressor cells (MDSCs) for 3.5 months after sepsis induction. Sepsis induced an increase in IL-10⁺ B cells, which was enhanced and prolonged by IL-7 treatment. An increased frequency of MDSCs in the spleen was still detectable 3.5 months after sepsis induction and this was more pronounced in IL-7-treated mice. MDSCs from septic mice were more potent at suppressing T cell proliferation than MDSCs from control mice. Our data reveal that sepsis induces a long lasting increase in IL-10⁺ B cells and MDSCs. Late-onset IL-7 treatment augments this increase, which should be relevant for clinical interventions.</p></div

Sepsis results in sustained activation of DN T cells.

<p>Mice were injected with PBS i.p. (Sham) or subjected to sepsis induction. IL-7 (Sepsis + IL-7) or PBS (Sepsis + PBS) was injected daily for 5 days from day 5–9 post sepsis induction. The cytokine expression in CD3⁺NK1.1^-γδTCR^-CD4^-CD8^- (double negative, DN) T cells from the spleen was analysed 1 week, 1 month and 3.5 months after sepsis induction. <b>(A)</b> Representative flow cytometry images from analysis after 1 week showing DN T cells and IFN-γ and IL-10 expression. <b>(B)</b> Frequency of DN T cells among CD3⁺ cells (left) and their absolute numbers (right). <b>(C)</b> Frequency of IFN-γ⁺ cells among DN T cells (left) and their absolute numbers (right). <b>(D)</b> Frequency of IL-10⁺ cells among DN T cells (left) and their absolute numbers (right). n = 7–13 (1 week), 5–10 (1 month), 3–6 (3.5 months) for IL-10 staining and 3–12 (3.5 months) for IFN-γ staining. *<i>P</i>< 0.05, **<i>P</i>< 0.01, ***<i>P</i>< 0.001 (ANOVA). Data are expressed as mean ± SEM. Data are representative of three experiments for the sham and sepsis + PBS groups. Data are representative of two experiments for the sepsis + IL-7 group.</p

Sepsis results in a sustained expansion of MDSCs.

<p>Mice were injected with PBS i.p. (Sham) or subjected to sepsis induction. IL-7 (Sepsis + IL-7) or PBS (Sepsis + PBS) was injected daily for 5 days from day 5–9 post sepsis induction. Gr1⁺CD11b⁺ cells from the spleen and bone marrow were analysed 1 week, 1 month and 3.5 months after sepsis induction. <b>(A, B)</b> Representative flow cytometry images from spleen (A) and bone marrow (B) from analysis after 3.5 months. <b>(C)</b> Frequency of Gr1⁺CD11b⁺ cells among total spleen cells (top) and among total bone marrow cells (bottom). <b>(D)</b> Number of Gr1⁺CD11b⁺ cells in spleen (top) and bone marrow (bottom). n = 6–9 (1 week), 5–12 (1 month), 8–20 (3.5 months). *<i>P</i>< 0.05, **<i>P</i>< 0.01, ***<i>P</i>< 0.001 (ANOVA). Data are expressed as mean ± SEM. Data are representative of three experiments.</p