Intake, ingesta retention, particle size distribution and digestibility in the hippopotamidae

Although several aspects of the digestive physiology of the hippopotamidae-non-ruminating foregut fermenters-have been described, ingesta kinetics and passage characteristics of these species are not well understood. The most outstanding feature of the hippo digestive physiology reported so far is the very long mean ingesta retention times (MRTs) measured by Foose [Foose, T., 1982. Trophic strategies of ruminant versus nonruminant ungulates. PhD dissertation, University of Chicago, Chicago.]. Since those data had been investigated with animals without water access, we intended to measure MRT in hippos which were allowed to enter water pools during the night. MRT parameters as well as dry matter (DM) digestibility were determined in four common (Hippopotamus amphibius) and four pygmy hippos (Hexaprotodon liberiensis) on two different diets each using cobalt ethylendiamintetraacetate (Co-EDTA) as a fluid, chromium (Cr)-mordanted fibre (<2 mm) as a particle and acid detergent lignin (ADL) as an internal digestibility marker. Four of the animals additionally received cerium (Ce)-mordanted fibres (2-10 mm) as particle markers. Total MRTs for fluids and particles ranged between 20-35 and 48-106 h in the common and between 13-39 and 32-107 h in the pygmy hippos. The difference between fluid and particle retention was greater than usually reported in ruminants. Excretion patterns of the markers differed from those usually observed in ruminants but resembled those reported for macropods (kangaroos), indicating a plug-flow reactor-like physiology in the hippo forestomach (FRST). This finding complements other described similarities between the macropod and the hippo forestomach. The measurements of larger particle retention profiles suggest that in the hippo, larger particles might be excreted either faster or at the same rate as smaller particles, indicating a general difference between ruminants and hippos with respect to differential particle retention. The digestive physiology of hippos is characterised by a generally low food intake, long ingesta retention times and dry matter digestibilities lower than reported in ruminants. Moderate digestibilities in spite of long retention times might be the result of the generally high average ingesta particle size in hippos. The comparatively easy management of pygmy hippos, together with the significant correlations between food intake, MRT and digestibility in the pygmy hippos of this study, recommends this species for further studies on the interplay of these parameters in herbivore digestive physiology.     

Retention of different-sized particles and derived gut fill estimate in tammar wallabies (Macropus eugenii): physiological and methodological considerations

The capacity of the digestive tract is an important parameter in understanding digestive adaptations, particularly in herbivores. Measures of this capacity (‘gut fill’) are commonly performed in killed animals, which has ethical and logistical implications. Alternatively, dry matter gut contents (DMC) can be estimated in live animals from food intake, digesta retention and digestibility, based on physical principles (Holleman and White, Can. J. Zool. 67, 488-494, 1989). Although this method has been used to some extent, it still awaits thorough validation. Here we estimated DMC in seven tammar wallabies during 5-day feeding trials and compared the results to those gained from dissections immediately after the trials. Calculated DMC exceeded that actually measured by 29 ± 22%. A closer inspection of the data suggested that this was partly due to the fact that DMC as measured by dissection is susceptible to short-term influences such as daily variation in food intake, whereas the calculated DMC represents an integrative measure over the whole period of the feeding trial. Correlations between both the measured digesta retention times, and the calculated DMC, with the measured wet contents mass suggest that it is particularly the DMC determined via dissection that needs to be measured with care. For a comparison of gut capacities, the calculated DMC therefore can be considered adequate, but should for a more widespread use be validated in further studies including more species and experimental regimes controlling food intake variation. Additionally, we tested whether very small (100-500 μm) and small (500-1000 μm) particles were retained differently in the tammar wallabies. There was no indication of such a difference. Whether the macropod forestomach selectively passes a certain particle fraction (that represents microbes) with the generally faster-passing fluids remains to be investigated with even smaller markers, e.g. labelled bacteria.     

Dispersal and recruitment dynamics in the fleshy‐fruited Persoonia lanceolata (Proteaceae)

Question: What is the role of dispersal, persistent soil seed banks and seedling recruitment in population persistence of fleshy‐fruited obligate seeding plant species in fire‐prone habitats? Location: Southeastern Australia. Methods: We used a long‐term study of a shrubby, fleshy‐fruited Persoonia species (Proteaceae) to examine (1) seed removal from beneath the canopy of adult plants; (2) seedling recruitment after fire; (3) the magnitude and location of the residual soil seed bank; and (4) the implications for fire management of obligate seeding species. We used demographic sampling techniques combined with Generalised Linear Modelling and regression to quantify population changes over time. Results: Most of the mature fruits (90%) on the ground below the canopy of plants were removed by Wallabia bicolor (Swamp wallaby) with 88% of seeds extracted from W. bicolor scats viable and dormant. Wallabies play an important role in moving seeds away from parent plants. Their role in occasional long distance dispersal events remains unknown. We detected almost no seed predation in situ under canopies (< 1%). Seedling recruitment was cued to fire, with post‐fire seedling densities 6‐7 times pre‐fire adult densities. After fire, a residual soil seed bank was present, as many seeds (77‐100%) remained dormant and viable at a soil depth where successful future seedling emergence is possible (0‐5 cm). Seedling survival was high (> 80%) with most mortality within 2 years of emergence. Plant growth averaged 17 cm per year. The primary juvenile period of plants was 7–8 years, within the period of likely return fire intervals in the study area. We predicted that the study population increased some five‐fold after the wildfire at the site. Conclusions: Residual soil seed banks are important, especially in species with long primary juvenile periods, to buffer the populations against the impact of a second fire occurring before the seed bank is replenished.     

Molecular cloning and characterization of the polymorphic<Emphasis Type="Italic"> MHC</Emphasis> class II<Emphasis Type="Italic"> DBB</Emphasis> from the tammar wallaby (<Emphasis Type="Italic">Macropus eugenii</Emphasis>)

Genes of the major histocompatibility complex (MHC) have been characterized in all extant lineages of mammals. The tammar wallaby (Macropus eugenii) is well established as a model marsupial species; however, no classical MHC sequences have been described from this species. We have isolated two MHC class II -chain sequences from a tammar wallaby spleen cDNA library using a tammar MHC class II probe. These sequences belong to the marsupial MHC class II DBB gene family. Two additional DBB sequences were amplified from tammar wallaby genomic DNA. All four sequences were obtained from the same individual, indicating that there are at least two DBB loci in the tammar wallaby.Nucleotide sequence data reported are available in the GenBank database under the accession numbers AY438038–AY438042     

Body condition of the red kangaroo (Macropus rufus) in arid Australia: The effect of environmental condition,sex and reproduction

The body condition of live-caught male and female red kangaroos (Macropus rufus Desmarest 1842) was assessed in environmental conditions described by a period of high (two years) followed by low (one year) rainfall. Changes in pasture biomass and quality closely followed rainfall fluctuations in these years. Fluctuations in standardized body mass, in turn, lagged behind changes in pasture biomass with a delay of three months. Male and female body condition was best predicted by green grass biomass. Kangaroos caught during the high rainfall period reached an above average plane of condition. In the low rainfall period that followed, the condition of kangaroos declined, and was greater for small males (14–41 kg), large males (45–89 kg), and females (18–36 kg) with small or no pouch young than for female subadults (< 22 kg) and females with large pouch young (20–34 kg). Female subadults were also significantly older and the ratio of females:females with young-at-foot was higher in the low rainfall period. This suggests a mechanism for age/sex class differences in survivorship. The lagged synchrony of body condition with pasture biomass can be explained by body-size related digestive constraints, reflecting sex differences in adaptation to a stochastic environment.     

Ultrastructural observations of cryoinjury in kangaroo spermatozoa

Macropod spermatozoa have proven difficult to cryopreserve such that empirical studies using high concentrations of glycerol and/or DSMO have resulted in only 10% post-thaw motility. We examined the ultrastructure and freeze-fracture of caput and cauda epididymal macropod spermatozoa at 35, 4 degrees C and following cryopreservation with and without 20% glycerol. The addition of 20% glycerol resulted in significant damage to the sperm plasma membrane and mitochondria compared to no glycerol at the same temperatures (P<0.05). Following cryopreservation, 20% glycerol significantly improved the preservation of the cauda epididymal sperm plasma membrane and mitochondria and reduced the incidence of axonemal damage and axonemal spaces. For caput epididymal spermatozoa, glycerol only improved the preservation of the plasma membrane following cryopreservation (P<0.05). Freeze fracture microscopy revealed a pattern of helically wound intramembranous particles in the plasma membrane over the fibre network of the mid piece of the sperm tail. The fibre network is an interconnecting cytoskeletal structure found underneath the plasma membrane of the kangaroo sperm midpiece and is thought to add rigidity to the proximal portion of the sperm tail. After thawing, the plasma membrane was damaged such that this structure was missing in patches, and the helical rows of particles were mal-aligned. On the principal piece, particles were arranged randomly at physiological temperatures; however, upon cooling to 4 degrees C with 20% glycerol, the particles become aggregated. Once rewarmed (35 degrees C), particles over the principal piece resumed their random organisation. This finding is further evidence of a reversible phase transition of the macropod sperm plasma membrane during cooling that is not associated with a loss of motility or membrane integrity.