Small Litters Research Articles

Why is there discordant diversity in sengi (Mammalia: Afrotheria: Macroscelidea) taxonomy and ecology?

AbstractThe seventeen species of sengis or elephant‐shrews form a well‐defined clade of mammals endemic to Africa that occupy the extremes of terrestrial habitats, from coastal deserts to montane forests. Because of their isolation on Africa soon after the break‐up of Gondwanaland, theoretically sengis initially evolved with little competition from other placental radiations. Their life history features include myrmecophagy, saltatorial gaits, no or limited use of nests, social monogamy, small litters of precocial young and absentee maternal care of neonates. These traits together are unique to the Macroscelidea and represent a wedding of features usually associated with either small antelopes or anteaters. Combined, these features define an adaptive syndrome that presumably has been relatively immune to competition from contemporary mammals, partially due to phylogenetic inertia. Yet paradoxically, the syndrome is well suited to a wide range of terrestrial habitats, resulting in low taxonomic diversity. Because of their unusual phylogeny and low species diversity, conservation interest is high for those sengis with relatively low densities in fragmented forests.

Oogenesis defects in a mutant mouse model of oculodentodigital dysplasia

The essential role of connexin43 (Cx43) during oogenesis has been demonstrated by the severe germ cell deficiency and arrested folliculogenesis observed in Cx43 knockout mice. Recently, another mutant mouse strain became available (Gja1(Jrt)/+) that carries the dominant loss-of-function Cx43 mutation, Cx43(G60S). Gja1(Jrt)/+ mice display features of the human disease oculodentodigital dysplasia (ODDD), which is caused by mutations in the GJA1 gene. We used this new mutant strain to study how a disease-linked Cx43 mutant affects oogenesis. We found that female mutant mice are subfertile with significantly reduced mating success and small litters. The phosphorylated species of the Cx43 protein are reduced in the mutant ovaries in association with impaired trafficking and assembly of gap junctions in the membranes of granulosa cells, confirming that the mutant protein acts dominantly on its wild-type counterpart. Correspondingly, although starting with a normal abundance of germ cells, ovaries of the mutant mice contain significantly fewer pre-ovulatory follicles and do not respond to superovulation by gonadotropins, which is at least partially the result of reduced proliferation and increased apoptosis of granulosa cells. We conclude that the Gja1(Jrt) mutation has a dominant negative effect on Cx43 function in the ovary, rendering the females subfertile. Given these findings, closer examination of reproductive function in ODDD human females is warranted.

Tyrosylprotein Sulfotransferase-2 Expression Is Required for Sulfation of RNase 9 and Mfge8 in Vivo

Protein-tyrosine sulfation is mediated by two Golgi tyrosyl-protein sulfotransferases (TPST-1 and TPST-2) that are widely expressed in vivo. However, the full substrate repertoire of this enzyme system is unknown and thus, our understanding of the biological role(s) of tyrosine sulfation is limited. We reported that whereas Tpst1(-/-) male mice have normal fertility, Tpst2(-/-) males are infertile despite normal spermatogenesis. However, Tpst2(-/-) sperm are severely defective in their motility in viscous media and in their ability to fertilize eggs. These findings suggest that sulfation of unidentified substrate(s) is crucial for normal sperm function. We therefore sought to identify tyrosine-sulfated proteins in the male genital tract using affinity chromatography on PSG2, an anti-sulfotyrosine monoclonal antibody, followed by mass spectrometry. Among the several candidate tyrosine-sulfated proteins identified, RNase 9 and Mfge8 were examined in detail. RNase 9, a catalytically inactive RNase A family member of unknown function, is expressed only in the epididymis after onset of sexual maturity. Mfge8 is expressed on mouse sperm and Mfge8(-/-) male mice are subfertile. Metabolic labeling coupled with sulfoamino acid analysis confirmed that both proteins are tyrosine-sulfated and both proteins are expressed at comparable levels in wild type, Tpst1(-/-), and Tpst2(-/-) epididymides. However, we demonstrate that RNase 9 and Mfge8 are tyrosine-sulfated in wild type and Tpst1(-/-), but not in Tpst2(-/-) mice. These findings suggest that lack of sulfation of one or both of these proteins may contribute mechanistically to the infertility of Tpst2(-/-) males.

Phenotypic and genetic parameters and responses in temperament of silver fox cubs in a selection experiment for confident behaviour

A selection experiment for more confident silver foxes was arranged to find out possibilities to obtain selection response in confidence. Variation in aggressiveness and ease of capture was also studied. Fixed factors affecting the traits were studied using WSYS program. Covariances for breeding values were estimated with REML and multitrait animal models using VCE4 and Pest programs. It appeared that males were more confident than females. Cubs born in small litters tended to be more confident, less aggressive and easier to capture compared to those born in greater litters. Cubs of one-year-old dams seemed to be more confident and easier compared to those of older dams. Moderate estimate of heritability was obtained for confidence (h2 = 0.22). During three years of selection, genetic response of 0.13 points was achieved in confidence in selection line compared to control line. A higher selection differential existed in males than females. Predicted response of 0.21 points was slightly higher than the estimated one. No heritability was observed in aggressiveness, while a low one existed in ease of capture (h2 = 0.07). No association between confidence and the other behaviour traits were found.;

Infertile Boars with Knobbed and Immotile Short‐tail Sperm Defects in the Finnish Yorkshire Breed

In the period 1996-2006 two specific sperm defects, the knobbed acrosome (KA) defect and the immotile short-tail sperm (ISTS) defect, showed a strong negative association with fertility in Finnish breeding boars. In this study, we examined the incidence of these two sperm defects in two pig breeds, their effects on fertility and their associations with sperm morphology and testicular histology. Semen samples from 2048 (1097 Yorkshire, 951 Landrace) boars were collected. None of the Landrace boars revealed either the KA defect or the ISTS defect. Of the Yorkshire boars, 0.8% were afflicted with the KA defect and 7.6% with the ISTS defect. Boars diagnosed with the ISTS defect produced no litters. Fertility data were available from two artificially inseminated (AI) boars and six farm breeding boars affected with the KA defect. Breeding boars with 45-81% knobbed spermatozoa (n = 6) did not produce any litters out of 71 sows bred. AI boars with 25-30% knobbed spermatozoa had a poor non-return rate (on average 47% compared with 85% for normal control boars) and produced small litters, on average 2.5 piglets less than other boars of the same breed. Morphometry of testicular tissue and distribution of different cells in the seminiferous tubules were examined in nine boars. Boars with the KA defect had a smaller diameter of the seminiferous tubules (p < 0.05) and a lower number of Sertoli cells (p < 0.05) than controls. ISTS boars, in turn, had a significantly lower number of elongated spermatids (p < 0.05), and they also produced on average only 12% of the spermatozoa of normal boars. The ISTS defect is a manifestation of an autosomal recessive disease caused by an insertion in the KPL2 gene in porcine chromosome 16. Although we tried to map the KA defect, its aetiology remains unclear.

Impact of diet and stress on the development of preeclampsia-like symptoms in p57kip2 mice

The cyclin-dependent kinase inhibitor p57(kip2) regulates the cell cycle of trophoblastic cells. It has been established by a Japanese group that the heterozygous p57(kip2) knockout (p57(-/+)) mice are a good model of preeclampsia as they develop hypertension, proteinuria, and placental pathology. However, apart from the placental pathology, we could not observe these symptoms in our laboratory. Hence, we investigated the impact of diet and stress on this model. To do so, we compared the effects of the Japanese diet to that of the North American diet used by our animal facility. Furthermore, the impact of stress was determined by placing the mice in a restraining device before and at the end of gestation. Although the Japanese diet did not have any impact on blood pressure or proteinuria, the mice did develop endothelial dysfunction, left ventricular hypertrophy, as well as increased placental pathology. Also, all mice had smaller litters when fed the Japanese diet. However, stress response of these mice was not increased during gestation; in fact, a decrease was observed in the p57(-/+) mice, suggesting that this was probably not a player in the development of the pathology. Taken together, these results suggest that other environmental factors may have been implicated in the development of preeclampsia-like symptoms in this animal model. Moreover, we demonstrated that placental pathology and genetic factors are not sufficient to trigger preeclampsia-like symptoms in this model and that the diet might play an important part in the development of this multifactorial disease.

Particle size alters litter diversity effects on decomposition

Nutrient transfer between decomposing leaves may explain non-additive species diversity effects on decomposition. The influence of the diversity of litter species on decomposition was compared in mixtures composed of large (>200 mm 2) or small (<9 mm 2) litter fragments. The increase in the number of species (aspen, oak, alder and pine, from monocultures to four species in all possible combinations) initially (at day 43) suppressed respiration, but eventually (after 142 days) did not affect the mass loss of the mixtures of small litter fragments. In contrast, the decomposition of litter in large fragments increased with increased diversity, and 93% of all mixtures decomposed faster than would be predicted from monocultures. The results suggest that the active transport of nutrients by fungal hyphae, rather than passive diffusion, drives positive effect of the litter species diversity on decomposition.

Early Undernutrition Leads to Long-Lasting Reductions in Body Weight and Adiposity Whereas Increased Intake Increases Cardiac Fibrosis in Male Rats1,

Previous studies suggest that both overfeeding and undernutrition during development increase the risk of obesity and hypertension in adulthood. In this study, we examined both short- (24 d) and long- (16 wk) term effects of early postnatal over- and underfeeding in rats on body weight, body composition, plasma hormones, adiposity markers, and hypothalamic neuropeptide Y content. Cardiovascular changes were also examined by measuring blood pressure and cardiac fibrosis. Rats raised in litters of 3, 12, or 18 pups per mother were used to model early onset overfeeding, control, and underfeeding, respectively. At 24 d of age, pups raised in small litters (SL) were 10% heavier than pups from normal litters, accompanied by increased organ mass and fat mass, elevated plasma leptin, corticosterone, and uncoupling protein-1 mRNA in brown adipose tissue. On the other hand, pups raised in large litters were 17% lighter with no significant changes in plasma leptin. Overfeeding during the first 3 wk of life led to increased plasma leptin concentration in adulthood, whereas underfed rats remained significantly lighter throughout the study, with no evidence of catch-up growth. Rats raised in SL were more susceptible to developing cardiac fibrosis with a 22% increase in collagen deposition compared with control rats at 16 wk of age (P < 0.05). This was independent of any changes in blood pressure. This study demonstrates that nutritional changes early in postnatal development can have long-lasting effects on body weight, adiposity, and some mediators involved in energy homeostasis and can also lead to structural changes in the heart in adulthood. This highlights the importance of identifying potential early life risk factors involved in the modulation of childhood nutrition.

Effect of litter size and birth weight on naturally occurring myopia in the Labrador retriever

Abstract Purpose To evaluate early environmental influences (e.g. litter size, birth weight, birth season) on adult refractive error in dogs. A previous familial aggregation analysis has shown that the distribution of refractive error in a large family of pedigree Labrador Retrievers has a significant genetic component, but that litter size and other residual/environmental factors also have significant effects. Methods Refractive error was measured by cycloplegic retinoscopy in both eyes of 166 dogs, 1‐8 years of age and free of ocular pathology, from a large family of pedigree Labrador Retrievers. All dogs originated from the same breeding colony. The early records of these dogs included information on birth weight, maternal litter cohort, litter size and neonatal weight gain, measured daily for the first 6 weeks. These factors were analyzed to investigate their effect on adult refractive error. Results The average adult spherical equivalent refraction (SER) was ‐0.44D (‐5.38D to +1.65D, n = 166): 35% were myopic (SER ≤ ‐0.50D), 58% emmetropic (SER = ‐0.49 to +0.99) and 7% hyperopic (SER ≥ +1.00D). Mean birth weight was 421±57g. Higher birth weight was weakly (R=0.3) correlated with more hyperopic adult refractions. Relative to large litters (≥ 7), dogs from small litters (&lt; 7) gained more weight within the first 6 weeks of life and were on average 0.43D more myopic. Conclusion The dog provides a unique model for studying a wide range of environmental influences on the development of naturally occurring, high prevalence, low degree myopia.

Pragmatic management increases a flagship species, the Himalayan brown bears, in Pakistan’s Deosai National Park

Deosai Plateau in Northern Pakistan was designated a national park to protect the largest remnant population of brown bears in Pakistan. The natural resources of this high elevation (3500–5000 m) park make a significant contribution to the livelihood of local and nomad communities. The present legislation excludes people from a park, which increases conflicts between management and local people. However, a pragmatic approach was adopted to involve people in conservation in Deosai. Community participation, achieved by recognizing rights and introducing incentives, reduced resistance against the conservation efforts, reduced grazing pressure in bear habitat and helped reduce poaching. The size of the brown bear population was set as an indicator of park success, and was monitored annually from 1993 through 2006. We observed a 5% annual growth of the brown bear population, suggesting that the conservation program has been successful due to a successful cooperation between an NGO, people, and the park management. The increase of the bear population is significant, because we observed an extremely low reproductive rate, due to late age of first reproduction (8.25 years), a long reproductive interval (5.7 years), and a small litter size (1.33). The reproductive rate of the Deosai population is the lowest yet documented for brown bear populations. Poor habitat quality, low quality food, high seasonality, and extreme weather conditions in the Himalaya probably explain the poor reproductive performance. Considering such low reproduction and known exchange of individuals with neighboring populations, we believe that the observed growth was a sum of reproduction and immigration. Brown bears are declining throughout South Asia and often have low-productive rates. Therefore, conservation efforts for brown bears in this region must target reducing human-caused mortalities, particularly of adult females. Involvement of people can increase efficiency in conservation, in addition to reducing cost and conflicts.

Relationship between litter characteristics and female size in Tityus stigmurus (Scorpiones, Buthidae)

Abstract Tityus stigmurus (Thorell 1876) is one of the most medically important scorpion species in Brazil, but many basic aspects of its life history are unknown. Here the pattern of female reproductive investment was examined, along with development of the 1st and 2nd instars and the relationship between 2nd instar mass and molting to the 3rd instar. Relative to other buthid scorpions, T. stigmurus has a smaller litter (average 10 young) and a shorter 1st-instar period (average 4 days) and 2nd-instar period (average 68 days). Neither litter size nor offspring mass showed a relationship to female size. A significant positive correlation was observed between total litter mass and litter size. The minimum mass required for successful molting to the 3rd instar was 34.0 mg. Overall, female reproductive resources in T. stigmurus appear to be applied to the production of more but not heavier offspring.

Effect of litter size and birth weight on growth, carcass and pork quality, and their relationship to postmortem proteolysis1

The objective of the study was to test the hypothesis that birth weight (BtW) influences growth, carcass characteristics, meat quality, and postmortem (pm) proteolysis differently when pigs originate from small (S) or large (L) litters. Swiss Large White barrows (60) used in this study originated from 20 litters with either less than 10 (S) or more than 14 (L) piglets born per litter. Within each of the S and L litters, 3 barrows were selected at birth: the lightest (L-BtW), the heaviest (H-BtW), and the one with a BtW nearest to the average BtW of the litter (M-BtW). The BW and total feed intake of the individually penned pigs were determined weekly. At slaughter, carcass characteristics were assessed. Meat quality traits were determined in the LM and dark portion of semitendinosus muscle. Titin, nebulin, desmin, and integrin proteolysis were evaluated by SDS-PAGE and Western blot technique, and mu - and m-calpain activities were monitored using casein zymography. Litter size affected BtW of L-BtW and M-BtW but not of H-BtW barrows (BtW x litter size interaction; P = 0.07). From weaning to slaughter, L-BtW barrows grew slower (P < 0.01), ingested less feed (P < 0.01), and were less efficient (P < 0.01) than H-BtW and M-BtW barrows. The carcass yields were greater (P < 0.01), and livers and kidneys were lighter (P </= 0.01) in L-BtW compared with H-BtW barrows. Regardless of BtW, barrows from S litters had greater percentages of shoulder (P = 0.02) and lower percentages of omental fat (P = 0.06) than barrows from L litters. Compared with the LM of H-BtW barrows, the LM of L-BtW barrows was redder (P < 0.01). The semi-tendinosus muscle of M-BtW barrows was more (P < 0.01) tender than that of L-BtW and H-BtW barrows. The extent of titin and nebulin proteolysis at 24 and 72 h pm was greater (P </= 0.07) in the LM of H-BtW than in L-BtW barrows. At 72 h pm, integrin of the LM had been less (P = 0.08) degraded in barrows originating from S than from L litters. These results confirm the known effect of BtW on growth performance, whereas its effect on carcass characteristic and meat quality traits could only be partially demonstrated. Although litter size affected average BtW of the L-BtW and M-BtW barrows, its effect on growth performance, carcass characteristics, and meat quality was minor. The almost complete absence of significant BtW x litter size interaction indicates that litter size affects swine growth and carcass and meat quality through its inverse relationship with BtW.

Intestinal microflora and obesity in rats

The relationship was evaluated between early nutritional experiences, the intestinal microflora and the small intestinal functions in the mechanism of predisposition to obesity development. Male Sprague-Dawley rats were used in which the quantity of nutrition was manipulated from birth to weaning (day 30) by adjusting the number of pups in the nest to 4 small litters (SL) and 10 normal litters (NL) and fed a standard diet from days 30 to 40 of age. After 40 d, the postnatally overfed SL pups became heavier, displayed significantly enhanced adiposity, body mass gain and food intake as well as a significantly higher jejunal alkaline phosphatase and maltase activity than in rats nursed in NL nests. The effect of different early nutrition was also accompanied by the appearance of significantly decreased Bacteroides and significantly increased enterococci and lactobacilli of obese rats than in lean NL rats. The amounts of Bacteroides were negatively correlated with fat pad mass, body mass, body-mass gain and food intake whereas enterococci and lactobacilli were correlated positively with the same parameters. Our results demonstrate that postnatal nutritional experience may represent a predisposing factor influencing ontogeny of small intestine function and development of intestinal microbial communities. The acquired changes and associated alterations in food digestion could be a component of regulatory mechanisms contributing to the development of obesity and its maintenance in later life.

Extensive nonhomologous meiotic synapsis between normal chromosome axes of an rcp(3;6)(p14;q21) translocation in a hairless Mexican boar

Due to its low fertility, expressed as small litter size, a Mexican hairless boar was subjected to cytogenetic investigation. Analysis of G-banded mitotic chromosomes revealed a reciprocal chromosome translocation, rcp(3;6) (p14;q21). Synaptonemal complex analysis showed a regular pairing behavior of the translocation chromosome axes, always resulting in a quadrivalent configuration. However, due to extensive nonhomologous pairing between the axes of nonderivative chromosomes 3 and 6, the quadrivalent mostly had an asymmetrical cross-shaped morphology. The nonhomologous pairing occurred not only at mid and late pachytene, but also at the earliest stage of pachytene. It seems that early pachytene heterosynapsis is a common phenomenon in the pairing behavior of pig reciprocal translocations. Therefore, heterosynapsis may reduce apoptosis of germ cells due to partial absence of homologous synapsis during the pairing phase of meiosis. The frequency of spermatocytes showing quadrivalent configurations with unpaired axial segments apparently did not affect germ cell progression in the boar, since fairly normal testicular histology was noticed.

Physicochemical Characteristics and Fatty Acid Composition of the Meat from Korean Native Black Pig with Different Slaughter Weight

The Korean native black pig (KNP) have several desirable meat qualities, which are highly demanded by Koreans in spite of its slow growth rate, low feed efficiency, and small litter size. The aim of this study was to evaluate meat quality and fatty acid composition of KNP at different slaughter weight in order to provide information to industry. Ninety female KNP of the same age (220 days) were divided into three groups by live body weights (30 pigs per each group); live weight of 50～59 ㎏ (T1), 60～69 ㎏ (T2) and 70～80 ㎏ (T3), respectively. After slaughtering the longissimus dorsi muscle (LD) and backfat from each group were obtained after 24 hr chilling. Crude protein content and shear force of LD from T3 was higher than that from T1 and pH of LD was significantly lower in that from T1 than from T2 and T3. Color measurement indicated that LD of T2 group had a higher L*-value and lower a*-value than those of T1 and T3. Slaughter weight of KNP generally did not affect the fatty acid composition of LD and backfat but the content of oleic acid (C18:1) of T2 in LD was significantly higher than those of T1 and T3. The results may provide basic information to industry to promote the production and processing of KNP, and assist in meeting the Korean consumer's demand.

Differences in patches of retention among leaves, woods and small litter particles in a headwater stream: the importance of particle morphology

The location of retention in the channel can influence invertebrate assemblage and breakdown processes associated with a litter particle in heterogeneous streams. We previously identified four types of litter patches that formed on riffles or different locations in pools (middle, edge, alcove), and demonstrated that middle patches had higher litter processing rates than the other patches. In this study, we examined differences in retention on the four patch types among leaves, woody materials and small litter particles, and among leaves of different sizes, by sampling natural and manipulated litter particles that were newly retained. Proportionally more woody materials, leaf pieces (16–50 mm) and particulate organic matter (1–16 mm) than leaves (>50 mm) were retained on middle patches, while proportionally more leaves than the other litter particles were retained on riffle and edge patches. The retention pattern of leaf species with different leaf sizes and a released experiment of leaf particles revealed that proportionally more leaf particles with smaller sizes were retained on middle patches. The flexibility, shape and dryness of litter particles also seem to affect the location of retention in the channel. These results suggest that the morphology of litter particles have the potential to affect the biological use and breakdown of litter particles through determining the location of retention within the channel. The size of leaves and processes that alter leaf size may have important roles on the breakdown and utilisation by invertebrates in these heterogeneous streams.

Stillborns, partially monosomic and partially trisomic, in the offspring of a boar carrying a translocation: rcp(14;15)(q29;q24).

Smaller liters and an increased rate of stillbirth were observed among the offspring of a boar carrying a reciprocal translocation, rcp(14;15)(q29;q24). The translocation appeared to be of de novo origin since, according to the owner, the sire and dam of the proband boar both produced normal-sized litters and no stillbirths. The increased rate of stillbirth among offspring of the proband was due to the production of zygotes partially monosomic for chromosome 14 (14q29-qter) and partially trisomic for chromosome 15 (15q24----qter). Three out of 4 such stillborn piglets had a cleft palate. One of the 4 also had a cardiac septal defect. Two partially monosomic and partially trisomic foetuses recovered at 95 days' pregnancy appeared patho-anatomically normal. The smaller litters were assumed to be due to an early wastage of embryos having other types of unbalanced karyotypes caused by the reciprocal translocation.

Reciprocal chromosome translocation with transfer of centromeric heterochromatin in the domestic pig karyotype.

Gustavsson, I. and Settergren, I. 1984. Reciprocal chromosome translocation with transfer of centromeric heterochromatin in the domestic pig karyotype. —Hereditas 100: 1–5 Lund, Sweden. ISSN 0018–0661. Received March 11. 1983 A boar with normal sexual behaviour and normal semen picture but producing half the normal litter size was found to be the carrier of a rcp(7q-;llq+). Several of his daughters in commercial herds were reported to farrow small litters. The translocation was also found in the sire of the boar, which demonstrated a fairly normal fertility and had been used extensively for breeding work. One of the chromosome breakages had occurred proximally in the q arm of chromosome 11 close to the centromere, with the transfer of centromeric heterochromatin to the chromosome arm 7q-. There was a ring-shaped quadrivalent in male meiosis, indicating a preferential 2:2 segregation. All offspring demonstrated normal or balanced heterozygous karyotypes in a 1:1 ratio.

Ultrasonographic Study of Deep Portion of Diencephalo‐Telencephalic Vesicle for the Determination of Gestational Age of the Canine Foetus

The aim of this study was to evaluate the accuracy of ultrasonographic measurement of the deep portion of diencephalo-telencephalic vesicle (DPTV) in the prediction of delivery date in different size bitches. The effects of litter size and foetal sex ratio on the accuracy were also investigated. For this purpose, the growth curve of DPTV was derived in large size dogs (26-40 kg) and the results of the accuracy of the prediction were compared with those obtained in small (< or =10 kg) and medium (11-25 kg) size dogs by the application of the equations derived from the growth curve previously described. Ultrasonographic examinations were performed once a week during the second half of pregnancy in seven large size bitches (26-40 kg body weight). A linear regression model was adopted to analyse the relationship between the DPTV mean values and the days remaining to parturition. The results of regression analysis indicated that DPTV measurement in large size dogs is significantly and linearly related to the gestational age. Ultrasonographic measurements of DPTV were also performed during pregnancy in different size bitches with unknown breeding dates. Although the results indicated a similar accuracy of the prediction of the date of parturition in the different sizes of bitches, a higher accuracy was obtained in normal and large litter size compared with small litters. Foetal sex ratio did not affect the accuracy. In conclusion, this study demonstrated that the accuracy of the prediction of parturition day obtained by ultrasonographic evaluation of DPTV growth is reliable when specific formulae for different size dogs are applied. It should be noted that although foetal sex ratio does not affect the accuracy, the prediction could be less accurate when a small litter is present.

Vocal mother-offspring communication in guinea pigs: females adjust maternal responsiveness to litter size.

BackgroundIn parent-offspring communication, vocal signals are often used to attract attention and offspring might call to induce parental behaviour. In guinea pigs (Cavia aperea f. porcellus) mothers wean larger litters later than small ones, but it is unknown whether this difference depends on processes induced during pregnancy or is influenced post-natally by the number of pups present. We here tested with playback-experiments using pup separation calls whether mothers with cross-fostered large experimental litters (four-pup-litters) were more responsive to offspring calls and maintained responsiveness for longer than mothers with small experimental litters (two-pup-litters). Mothers were tested when two pups were suckling i.e. when both teats were occupied.ResultsMothers of four-pup litters responded stronger to broadcast pup separation calls than those with two-pup litters. Additionally, we tested the mothers' responsiveness to pup separation calls in the absence of their pups on day 8 and 20 of lactation. Mothers of four-pup litters responded stronger and showed no decrease in responsiveness from day 8 to 20, whereas mothers of two-pup litters responded less and decreased responsiveness from day 8 to 20. Mothers of four-pup litters also weaned their pups 5 days later than those of two-pup litters.ConclusionMeasured by their response to pup calls and by time to weaning, guinea pig mothers adjust maternal responsiveness to litter size. This behaviour is likely to be an adaptive strategy in resource allocation during reproduction.