Gut microbiome differences between wild and captive black rhinoceros – implications for rhino health

A number of recent studies have shown the importance of the mammalian gut microbiome in host health. In the context of endangered species, a few studies have examined the relationship between the gut microbiome in wild versus captive populations due to digestive and other health issues. Unfortunately, the results seem to vary across taxa in terms of captive animals having higher, lower, or equivalent microbiome diversity relative to their wild counterparts. Here, we focus on the black rhinoceros as captive animals suffer from a number of potentially dietary related health effects. We compared gut microbiomes of wild and captive black rhinos to test for differences in taxonomic diversity (alpha and beta) and in functional diversity of the microbiome. We incorporated a more powerful metagenomic shotgun sequencing approach rather than a targeted amplification of the 16S gene for taxonomic assignment of the microbiome. Our results showed no significant differences in the alpha diversity levels between wild and captive black rhinos, but significant differences in beta diversity. We found that bacterial taxa traditionally associated with ruminant guts of domesticated animals had higher relative abundances in captive rhinos. Our metagenomic sequencing results suggest that unknown gut microbes of wild rhinos are being replaced by those found in conventional human-domesticated livestock. Wild rhinos have significantly different functional bacterial communities compared to their captive counterparts. Functional profiling results showed greater abundance of glycolysis and amino acid synthesis pathways in captive rhino microbiomes, representing an animal receiving sub-optimal nutrition with a readily available source of glucose but possibly an imbalance of necessary macro and micronutrients. Given the differences observed between wild and captive rhino gut microbiomes, we make a number of recommendations for potentially modifying captive gut microbiome to better reflect their wild counterparts and thereby hopefully improve overall rhino health in captivity

Gut microbiome differences between wild and captive black rhinoceros - implications for rhino health.

CITATION: Gibson, K. M., et al. 2019. Gut microbiome differences between wild and captive black rhinoceros – implications for rhino health. Scientific Reports, 9:7570, doi:10.1038/s41598-019-43875-3.The original publication is available at https://www.nature.comA number of recent studies have shown the importance of the mammalian gut microbiome in host health. In the context of endangered species, a few studies have examined the relationship between the gut microbiome in wild versus captive populations due to digestive and other health issues. Unfortunately, the results seem to vary across taxa in terms of captive animals having higher, lower, or equivalent microbiome diversity relative to their wild counterparts. Here, we focus on the black rhinoceros as captive animals suffer from a number of potentially dietary related health effects. We compared gut microbiomes of wild and captive black rhinos to test for differences in taxonomic diversity (alpha and beta) and in functional diversity of the microbiome. We incorporated a more powerful metagenomic shotgun sequencing approach rather than a targeted amplification of the 16S gene for taxonomic assignment of the microbiome. Our results showed no significant differences in the alpha diversity levels between wild and captive black rhinos, but significant differences in beta diversity. We found that bacterial taxa traditionally associated with ruminant guts of domesticated animals had higher relative abundances in captive rhinos. Our metagenomic sequencing results suggest that unknown gut microbes of wild rhinos are being replaced by those found in conventional human-domesticated livestock. Wild rhinos have significantly different functional bacterial communities compared to their captive counterparts. Functional profiling results showed greater abundance of glycolysis and amino acid synthesis pathways in captive rhino microbiomes, representing an animal receiving sub-optimal nutrition with a readily available source of glucose but possibly an imbalance of necessary macro and micronutrients. Given the differences observed between wild and captive rhino gut microbiomes, we make a number of recommendations for potentially modifying captive gut microbiome to better reflect their wild counterparts and thereby hopefully improve overall rhino health in captivity.https://www.nature.com/articles/s41598-019-43875-3Publisher's versio

Slow freezing, but not vitrification supports complete spermatogenesis in cryopreserved, neonatal sheep testicular xenografts.

The ability to spur growth of early stage gametic cells recovered from neonates could lead to significant advances in rescuing the genomes of rare genotypes or endangered species that die unexpectedly. The purpose of this study was to determine, for the first time, the ability of two substantially different cryopreservation approaches, slow freezing versus vitrification, to preserve testicular tissue of the neonatal sheep and subsequently allow initiation of spermatogenesis post-xenografting. Testis tissue from four lambs (3-5 wk old) was processed and then untreated or subjected to slow freezing or vitrification. Tissue pieces (fresh, n = 214; slow freezing, then thawing, n = 196; vitrification, then warming, n = 139) were placed subcutaneously under the dorsal skin of SCID mice and then grafts recovered and evaluated 17 wk later. Grafts from fresh and slow frozen tissue contained the most advanced stages of spermatogenesis, including normal tubule architecture with elongating spermatids in ~1% (fresh) and ~10% (slow frozen) of tubules. Fewer than 2% of seminiferous tubules advanced to the primary spermatocyte stage in xenografts derived from vitrified tissue. Results demonstrate that slow freezing of neonatal lamb testes was far superior to vitrification in preserving cellular integrity and function after xenografting, including allowing ~10% of tubules to retain the capacity to resume spermatogenesis and yield mature spermatozoa. Although a first for any ruminant species, findings also illustrate the importance of preemptive studies that examine cryo-sensitivity of testicular tissue before attempting this type of male fertility preservation on a large scale

Total cell viability of neonatal lamb testis tissue immediately after castration (fresh), cryopreserved by slow freezing and vitrification.

<p>Values represent mean ± SD of three donors (three replicates per donor). Lines above the error bars denote significance.</p

Xenograft volume density traits for pieces of lamb testis transplanted fresh (control) versus after slow freezing and thawing versus vitrification and thawing.

<p>For each assessed metric, data for the slow freezing group were no different (<i>P</i>>0.05) from the control. Within a trait, lines above the error bar denote significance.</p

Morphology of lamb testis pieces that were retained fresh (A) versus those subjected to slow freezing and thawing (B) versus those that were vitrified and thawed (C).

<p>All then were xenografted into SCID mice before excision and evaluation at 17 wk. Sections were stained with hematoxylin-eosin. Each scale bar = 100 μm.</p

Prevalence of advanced germ cell type per seminiferous cord/tubule cross-sections in xenografts that originally were fresh controls versus those subjected to slow freezing versus vitrification.

<p>The latter treatment resulted in production of mostly spermatogonial cells and primary spermatocytes in contrast to slow freezing where few immature germ cells remained along with a higher proportion of more advanced cell types, including elongated spermatids. Within a trait, lines above the error bar denote significance.</p

Histological appearance of immature lamb testis tissue exposed to one of three conditions.

<p>(A) control (fresh), (B) slow freezing and then thawing or (C) vitrification and then thawing (400x). Inset in each panel depicts the seminiferous cords (SC) at a higher magnification. Slow freezing preserved normal SC integrity similar to the fresh control, whereas vitrification caused disruptions, including evidence of shrinkage around the SC (*). G = gonocyte, S = Sertoli cell, M = peritubular myoid cell. Scale bar = 100 μm.</p