Data on linear sperm dimensions in mammals are presented. There is information on a total of 284 species, representing 6.2% of all species; 17.2% of all genera and 49.2% of all families have some representation, with quantitative information missing only from the orders Dermoptera, Pholidota, Sirenia and Tubulidentata. In general, sperm size is inverse to body mass (except for the Chiroptera), so that the smallest known spermatozoa are amongst those of artiodactyls and the largest are amongst those of marsupials. Most variations are due to differences in the lengths of midpiece and principal piece, with head lengths relatively uniform throughout the mammals.

https://rep.bioscientifica.com/downloadpdf/journals/rep/75/1/jrf_75_1_019.pdf

On mammalian sperm dimensions.

Analysis of 40 semen samples collected by electroejaculation from 18 cheetahs revealed no major differences in seminal traits among Transvaal, South West (Namibia) or hybrid (Transvaal X South West) males. However, mean spermatozoal concentration (14.5 X 10(6) spermatozoa/ml of ejaculate) and percent motility (54.0%) were less in cheetahs than in domestic cats (147.0 X 10(6) spermatozoa/ml of ejaculate, 77.0% motility) subjected to the same electroejaculation regimen. On the average, cheetah ejaculates contained 71.0% morphologically abnormal spermatozoa compared to 29.1% aberrant spermatozoal forms in the domestic cat. These results indicate that seminal characteristics in the cheetah are markedly inferior compared to the domestic cat, particularly with respect to the incidence of pleiomorphic spermatozoa. Because a recent parallel study demonstrates that the cheetah lacks genetic variation, it appears likely that spermatozoal abnormalities are a genetic consequence of genomic homozygosity characteristic of this endangered species.

/pdf/unique-seminal-quality-in-the-south-african-cheetah-and-a-1fjyvqoov6.pdf

Unique seminal quality in the South African cheetah and a comparative evaluation in the domestic cat.

We have examined sperm morphology and dimensions in Eutherian mammals. In most Eutherians, sperm heads are round or oval and spermatozoa have short tails (average sperm length about 65 microns; range = 33-121 microns). Rodents, however, clearly depart from the typical Eutherian pattern in that they show a broad array of head morphs and an extreme range of sperm dimensions (35-250 microns). In order to trace the evolutionary changes that rodent sperm have undergone, we have used phylogenetic relationships based on biogeographical, morphological, chromosomal and genic data, and we have superimposed onto them the information available on sperm traits. Analyses were carried out for five rodent groups on which enough information was available. The evolutionary trends which emerged from these studies have two main points in common: throughout evolution spermatozoa have become enlarged and morphologically more complex, and this process seems to have taken place independently in different lineages. A general model was developed which outlines the different evolutionary pathways that rodent sperm have undergone. The adaptive significance of the increase in head complexity and the elongation of the sperm tail remains obscure. We have integrated information from evolutionary, physiological and behavioural studies to address this issue. We argue that two main selective forces may have favoured these changes: female selection within the reproductive tract and sperm competition. The female tract represents a formidable barrier for spermatozoa and its provides an environment where numerous interactions take place. The extent of these barriers and the complexity of these poorly understood interactions suggest that females may be exercising a strong selection, which may enable them to favour particular types of spermatozoa or ejaculates from particular males. Throughout their evolution males must have evolved adaptations to overcome these barriers, and the conflicting interests of choosy females. Sperm competition is a potent evolutionary force among mammals, which has influenced not only the evolution of sperm numbers but also changes in sperm dimensions. Thus, sperm competition has favoured the elongation of the sperm tail, which has led to the attainment of faster swimming speed, an important factor when sperm from rival males compete to reach the ova first.

The evolution of eutherian spermatozoa and underlying selective forces: female selection and sperm competition

1 Of the eight species of Ursidae, six are currently at risk of extinction and the remainder face significant risks to their future survival One of the greatest threats to bears is human-imposed environmental alteration (eg global warming, chemical pollutants, deforestation) An examination of the reproductive biology and phylogeny of the Ursidae reveals reproductive seasonality as a probable adaptation to adverse environmental conditions 2 Seven of the eight extant species exhibit distinct mating and birth seasons, with the most ancient species evolving facultative seasonality as an adaptation to the increasingly seasonal climate of the Pliocene The remainder of the extant species evolved during the Pleistocene glaciations, under conditions of severe seasonal food restriction Under these conditions, an obligate mode of seasonality emerged and persists to the present 3 Knowledge of the natural history of seasonal reproduction in the ursids and how it evolved in response to global climatic change provides a context for understanding the ramifications of current environmental change on the reproduction of these important species

Evolution of reproductive seasonality in bears

and Summary
The activity rhythm, reproductive cycle, and maintenance, social and reproductive behavior of a pair of captive giant pandas were studied at the National Zoological Park, Washington, D.C. Results from this study and the available literature indicate that:

1) Giant pandas are probably nocturnal, although they may be polycyclic in activity.
2) Males are more active than females, especially in locomotor behavior and scent-marking activity
3) Activity levels are inversely correlated with age.
4) There is a single annual estrous period of one to three days between March and June, preceded by conspicuous behavioral changes in the female consisting of a depressed appetite, increased restlessness and scent-marking, and increased vocalizing. Behavioral changes in the male are similar and are synchronized with the female reproductive cycle.
5) The major communicatory modes are through scent-marking and vocalizations. A variety of postures is used to deposit urine and anogenital gland secretions throughout the environment. Most of the major call types show considerable variation and grading; they are prominent during agonistic and reproductive activities. Visual signals are only poorly developed. Tactile contact is more frequent during social interactions than might be predicted, considering the solitary nature of the species. However, significant tactile contact may be limited to the initial stages of encounters, with avoidance and intolerance occurring thereafter.
6) Both the giant panda's copulatory posture and the temporal patterning of copulation (numerous short mounts and a brief ejaculatory intromission with a long inter-ejaculation interval) differ significantly from sexual behavior reported for other closely related carnivores. Observations suggest that the prior compatibility of a pair is essential for successful reproductive behavior.
7) Comparative data on giant panda reproduction suggest that the 140 day average gestation length (range: 122–163 days) includes a delay, either in implantation or early development. The neonatalimaternal weight ratio may be the smallest among the Eutherian mammals.
8) Three major reproductive characteristics—


(a) the occurrence of a weak estrus in the autumn in some females
(b) variability in the duration of the “gestation” period and
(c) survivorship of only one young despite a litter size of one to three young — and fossil evidence for a much wider previous geographic distribution, suggest that giant pandas may have had a more flexible and opportunistic reproductive strategy during their past evolutionary history, and have recently undergone K-selection, with increasing dietary and habitat specialization.

Ethology and Reproduction of Captive Giant Pandas (Ailuropoda melanoleuca)

Summary. Semen was collected by a standardized electroejaculation procedure from a giant panda on 4 occasions. Ejaculate volume, sperm count and % sperm motility were 2\m=.\3\p=n-\3\m=.\6ml, 62\p=n-\562\m=x\ 106 spermatozoa/ml and 45\p=n-\85%respectively. The results, although limited to a single male, suggested a seasonal influence on ejaculate and gonadal parameters with improved ejaculate volume, sperm motility and increased testicular size in the season proximate to the female's oestrous period. Frozen\p=n-\thawed spermatozoa were motile with no apparent abnormalities induced by the freezing procedure.

/pdf/electroejaculation-and-semen-analysis-and-freezing-in-the-at1ocmqbxf.pdf

J. G. Howard

Papers

Electroejaculation and semen analysis and freezing in the giant panda (Ailuropoda melanoleuca)