Evaluating habitat connectivity methodologies: a case study with endangered African wild dogs in South Africa

Context

In fragmented landscapes, connectivity between subpopulations is vital for species’ persistence. Various techniques are used to assess the degree of connectivity between habitat patches, yet their performance is seldom evaluated. Models are regularly based on habitat selection by individuals in resident populations, yet dispersers may not require habitat which supports permanent residence.

Objectives and methods

Using a database of African wild dog (Lycaon pictus) occurrence records in north-eastern South Africa (n = 576), we developed and compared ecological niche models (ENM) for wild dogs packs and dispersers. Additionally, we used least cost path (LCP) and current flow models to assess connectivity. Results were further validated using occurrence records (n = 339) for cheetah (Acinonyx jubatus).

Results and conclusions

The ENM for wild dog packs identified large but isolated patches of suitable habitat, while the disperser ENM had greater suitability values for areas in between highly suitable patches. Without disperser-specific data, models omitted large areas which were confirmed to have provided connectivity. Although models derived from a potentially subjective cost layer have been criticised, the current flow model outperformed the other connectivity techniques and provided the most meaningful predictions for conservation planning. We identified five priority conservation areas for wild dogs, two of which had a greater feasibility for recolonisation. The scarcity of disperser-specific data promotes models using habitat data for resident individuals but here we illustrate the pitfalls thereof. Our study provides insights into the performance of these frequently employed techniques and how they may affect conservation management decisions.

     

Large B-cell lymphoma in the colon and mesocolon of a Thoroughbred racehorse: Detection prior to development of clinical signs using clinicopathological markers of inflammation

In this report, we describe an investigation into the cause of chronic inflammation in a clinically normal 5-year-old racing Thoroughbred, finally confirmed to be associated with B-cell lymphoma. Over a 14-week period, the horse was regularly evaluated by sequential blood testing, revealing persistent inflammation of unknown origin, unresponsive to treatment. Eventually, an abdominal mass was identified by transabdominal ultrasound and rectal palpation. Surgical exploration revealed an extensive, invasive soft tissue mass in the abdomen. At post-mortem examination, a mass involving the colon, mesocolon and mesocolonic lymph node was sampled and confirmed as a large B-cell lymphoma by histopathology and immunohistochemistry. In cases of unexplained chronic inflammation in a horse, neoplasia should be considered as a possible aetiology.     

Dogs with acute myeloid leukemia or lymphoid neoplasms (large cell lymphoma or acute lymphoblastic leukemia) may have indistinguishable mediastinal masses on radiographs

Acute myeloid leukemia is an uncommon hematopoietic neoplasm of dogs that should be differentiated from lymphoid neoplasms, such as lymphoma, because of different treatment protocols and a worse prognosis. Thoracic radiography is performed frequently in dogs with suspected hematopoietic neoplasia, and detecting a mediastinal mass often prioritizes lymphoma as the most likely diagnosis. However, we have observed a mediastinal mass in several dogs with acute myeloid leukemia and hypothesized that (1) the frequency of a mediastinal mass was higher and (2) the size of the mass was larger in dogs with acute myeloid leukemia compared to dogs with lymphoid neoplasms. In this analytical study (observational, retrospective, and cross‐sectional), the sample population included 238 dogs with hematopoietic neoplasia. These dogs were divided into lymphoid (large cell lymphoma, acute lymphoblastic leukemia) and myeloid groups based on standard phenotyping tests. A mediastinal mass was detected during thoracic radiography in 73/218 (33%) and nine of 20 (45%) dogs in the lymphoid and myeloid groups (P = 0.21), respectively. The median size ratio of mediastinal mass to cardiac silhouette was 0.20 and 0.23 in the lymphoid and myeloid groups (P = 0.96), respectively. Additionally, we observed normal thoracic radiographs in 111/218 (51%) dogs in the lymphoid group and nine of 20 (45%) dogs in the myeloid group. In conclusion, acute myeloid leukemia should be considered when a mediastinal mass is detected during radiography in dogs with suspected hematopoietic neoplasia—but the presence or size of a mediastinal mass does not differentiate between myeloid and lymphoid neoplasms.     

Intrahippocampal septal grafts ameliorate learning impairments in aged rats

Grafts of fetal septal tissue rich in cholinergic neurons were implanted as a dissociated cell suspension into the depth of the hippocampal formation in aged rats with severe impairments in spatial learning abilities. After 2 1/2 to 3 months, the rats with grafts, but not the controls, had improved their performance in a spatial learning test. Their improvement was due, at least in part, to an increased ability to use spatial cues in the task. In all animals the grafts had produced an extensive acetylcholinesterase-positive terminal network in the surrounding host hippocampal formation. Thus, the action of cholinergic neurons in the graft onto elements in the host hippocampal circuitry may be a necessary, but perhaps not sufficient, prerequisite for the observed functional recovery.     

Pharmacokinetics of enrofloxacin after single-dose oral and intravenous administration in the American alligator (Alligator mississippiensis).

The pharmacokinetics of enrofloxacin administered orally and i.v. to American alligators (Alligator mississippiensis) at 5 mg/kg was determined. Plasma levels of enrofloxacin and its metabolite ciprofloxacin were measured using high-performance liquid chromatography and the resulting concentration versus time curve analyzed using compartmental modeling techniques for the i.v. data and noncompartmental modeling techniques for the oral data. A two-compartment model best represented the i.v. data. Intravenous administration of enrofloxacin resulted in an extrapolated mean plasma concentration of 4.19 +/- 4.23 microg/ml at time zero, with average plasma drug levels remaining above 1.0 microg/ml for an average of 36 hr. Plasma volume of distribution for i.v. enrofloxacin was 1.88 +/- 0.96 L/kg, with a harmonic mean elimination half-life of 21.05 hr and mean total body clearance rate of 0.047 +/- 0.021 L/hr/kg. Plasma levels of p.o. enrofloxacin remained below 1.0 microg/ml in all test animals, and average concentrations ranged from 0.08 to 0.50 microg/ml throughout the sampling period. Oral administration of enrofloxacin achieved a mean maximum plasma concentration of 0.50 +/- 0.27 microg/ml at 55 +/- 29 hr after administration, with a harmonic mean terminal elimination half-life of 77.73 hr. Minimal levels of ciprofloxacin were detected after both oral and i.v. enrofloxacin administration, with concentrations below minimum inhibitory concentrations for most susceptible organisms. On the basis of the results of this study, enrofloxacin administered to American alligators at 5 mg/kg i.v. q 36 hr is expected to maintain plasma concentrations that approximate the minimum inhibitory concentration for susceptible organisms (0.5 microg/ml). Enrofloxacin administered to American alligators at 5 mg/kg p.o. is not expected to achieve minimum inhibitory values for susceptible organisms.