Capacity of the medullary cavity of tibia and femur for intra-bone marrow transplantation in mice.

Intra-bone marrow transplantation (IBMT) has been adapted for mouse models to improve the seeding efficiency of transplanted hematopoietic stem and progenitor cells. Commonly used injection volumes for IBMT into the tibia differ between 10 and 40 µL even though considerable amounts of injected cells leak into the blood circulation immediately after injection. Injection of 3 µL trypan blue into the tibia of dead BALB/c mice showed staining in large vessels of hind limbs, even without supporting circulation. We therefore tested the effective capacity of the medullary cavity of dissected tibiae and femora of different mouse strains by bioluminescence imaging after injection of luciferase expressing cells. Cell leakage was already observed at 3 µL of injection volume and the measured emission rate increased significantly when 5 and 10 µL of volume with the same cell concentration were injected. Surprisingly, increasing injection volumes containing constant cell amounts resulted in comparable emission rates, suggesting a similar amount of leaked and absorbed cells independent of the injection volume. However, the absorption of a specific amount of injected cells could not be confirmed, as the ratio of leaked to absorbed cells was similar between IBMT that were performed with a constant injection volume containing either low or high cell amounts. In summary, for optimal cell transplantation via IBMT in mice we suggest to inject a high concentrated cell suspension with a maximum injection volume of 3 µL.

Sexual experience has no effect on male mating or reproductive success in house mice.

The ability to learn from experience can improve Darwinian fitness, but few studies have tested whether sexual experience enhances reproductive success. We conducted a study with wild-derived house mice (Mus musculus musculus) in which we manipulated male sexual experience and allowed females to choose between (1) a sexually experienced versus a virgin male, (2) two sexually experienced males, or (3) two virgin males (n = 60 females and 120 males). This design allowed us to test whether females are more likely to mate multiply when they encounter more virgin males, which are known to be infanticidal. We recorded females' preference and mating behaviours, and conducted genetic paternity analyses to determine male reproductive success. We found no evidence that sexual experience influenced male mating or reproductive success, and no evidence that the number of virgin males influenced female multiple mating. Females always copulated with both males and 58% of the litters were multiple-sired. Females' initial attraction to a male correlated with their social preferences, but neither of these preference behaviours predicted male reproductive success - raising caveats for using mating preferences as surrogates for mate choice. Male reproductive success was predicted by mating order, but unexpectedly, males that copulated first sired fewer offspring.

Naive tadpoles do not recognize recent invasive predatory fishes as dangerous.

Invasive alien predators (IAP) are spreading on a global scale-often with devastating ecological effects. One reason for their success may be that prey species fail to recognize them due to a lack of co-evolutionary history. We performed a comprehensive test of this "prey naiveté" hypothesis using a novel approach: we tested whether predator-naive tadpoles of the agile frog (Rana dalmatina) display antipredator behavior upon encountering chemical cues produced by native, invasive (established or recent) or allopatric fishes (four perciforms, four siluriforms, and two cypriniforms). We studied the influence of population origin on predator-detection ability by presenting chemical cues to predator-naive tadpoles that originated from fishless hill-ponds or fish-infested floodplain populations. Before trials, we fed fishes with tadpoles or an alternative food to test whether direct chemical cues from the predator's diet influences the tadpoles' recognition of potential predators. Tadpoles reduced their activity upon exposure to cues from native and long-established invasive perciforms, but not in response to recent invaders, allopatric predators, or to any siluriforms. Also, predators that were previously fed with tadpoles did not universally induce behavioral defensedefenses upon first encounter. Finally, tadpoles originating from isolated hill-ponds exhibited higher baseline activity and responded in weaker fashion than their conspecifics from floodplain populations, which co-exist with predatory fishes. Our results indicate that tadpoles may be vulnerable to invading predatory fishes due to their inability to recognize them as dangerous, though their ability to recognize invasive IAP may evolve rapidly, in fewer than 30 generations.

The relative importance of prey-borne and predator-borne chemical cues for inducible antipredator responses in tadpoles.

Chemical cues that evoke anti-predator developmental changes have received considerable attention, but it is not known to what extent prey use information from the smell of predators and from cues released through digestion. We conducted an experiment to determine the importance of various types of cues for the adjustment of anti-predator defences. We exposed tadpoles (common frog, Rana temporaria) to water originating from predators (caged dragonfly larvae, Aeshna cyanea) that were fed different types and quantities of prey outside of tadpole-rearing containers. Variation among treatments in the magnitude of morphological and behavioural responses was highly consistent. Our results demonstrate that tadpoles can assess the threat posed by predators through digestion-released, prey-borne cues and continually released predator-borne cues. These cues may play an important role in the fine-tuning of anti-predator responses and significantly affect the outcome of interactions between predators and prey in aquatic ecosystems. There has been much confusion regards terminology used in the literature, and therefore we also propose a more precise and consistent binomial nomenclature based on the timing of chemical cue release (stress-, attack-, capture-, digestion- or continually released cues) and the origin of cues (prey-borne or predator-borne cues). We hope that this new nomenclature will improve comparisons among studies on this topic.

Multiple paternity does not depend on male genetic diversity.

Polyandry is common in many species and it has been suggested that females engage in multiple mating to increase the genetic diversity of their offspring (genetic diversity hypothesis). Multiple paternity occurs in 30% of litters in wild populations of house mice, Mus musculus musculus, and multiple-sired litters are genetically more diverse than single-sired ones. Here, we aimed to test whether female house mice produce multiple-sired litters when they have the opportunity to produce genetically diverse litters. We assessed the rates of multiple paternity when females could choose to mate with two males that were genetically dissimilar to each other (i.e. nonsiblings and MHC dissimilar) compared with when females could choose to mate with two males that were genetically similar to each other (i.e. siblings and shared MHC alleles). Multiple mating may depend upon a female's own condition, and, therefore, we also tested whether inbred (from full-sibling matings) females were more likely to produce multiple-sired progeny than outbred controls. Overall we found that 29% of litters had multiple sires, but we found no evidence that females were more likely to produce multiple-sired litters when they had the opportunity to mate with genetically dissimilar males compared with controls, regardless of whether females were inbred or outbred. Thus, our findings do not support the idea that female mice increase multiple paternity when they have the opportunity to increase the genetic diversity of their offspring, as expected from the genetic diversity hypothesis.

Multiple paternity in wild house mice (Mus musculus musculus): effects on offspring genetic diversity and body mass.

Multiple mating is common in many species, but it is unclear whether multiple paternity enhances offspring genetic diversity or fitness. We conducted a survey on wild house mice (Mus musculus musculus), and we found that in 73 pregnant females, 29% of litters had multiple sires, which is remarkably similar to the 23-26% found in feral populations of Mus musculus domesticus in the USA and Australia, respectively. The question is: How has selection maintained multiple mating in these subspecies since the evolutionary divergence, ca. 2800-6000 years ago? We found no evidence that multiple paternity enhanced females' litter size, contrary to the fertility assurance or genetic benefits hypotheses. Multiple paternity was associated with reduced mean and variance in offspring body mass, which suggests that females allocate fewer resources or that there is increased intrauterine conflict in multiple-versus single-sired litters. We found increased allelic diversity (though not heterozygosity) in multiple-sired litters, as predicted by the genetic diversity hypothesis. Finally, we found that the dams' heterozygosity was correlated with the mean heterozygosity of their offspring in single-and multiple-sired litters, suggesting that outbred, heterozygous females were more likely to avoid inbreeding than inbred, homozygous females. Future studies are needed to examine how increased genetic diversity of litters and smaller mean (and variance) offspring body mass associated with multiple paternity affect offspring fitness.

Female partner preferences enhance offspring ability to survive an infection.

BACKGROUND: It is often suggested that mate choice enhances offspring immune resistance to infectious diseases. To test this hypothesis, we conducted a study with wild-derived house mice (Mus musculus musculus) in which females were experimentally mated either with their preferred or non-preferred male, and their offspring were infected with a mouse pathogen, Salmonella enterica (serovar Typhimurium). RESULTS: We found that offspring sired by preferred males were significantly more likely to survive the experimental infection compared to those sired by non-preferred males. We found no significant differences in the pathogen clearance or infection dynamics between the infected mice, suggesting that offspring from preferred males were better able to cope with infection and had improved tolerance rather than immune resistance. CONCLUSION: Our results provide the first direct experimental evidence within a single study that partner preferences enhance offspring resistance to infectious diseases.

Why do female mice mate with multiple males?

Females often show multi-male mating (MMM), but the adaptive functions are unclear. We tested whether female house mice (Mus musculus musculus) show MMM when they can choose their mates without male coercion. We released 32 females into separate enclosures where they could choose to mate with two neighboring males that were restricted to their own territories. We also tested whether females increase MMM when the available males appeared unable to exclude intruders from their territories. To manipulate territorial intrusion, we introduced scent-marked tiles from the neighboring males into males' territories, or we rearranged tiles within males' own territories as a control. Each female was tested in treatment and control conditions and we conducted paternity analyses on the 57 litters produced. We found that 46 % of litters were multiply sired, indicating that multiple paternity is common when females can choose their mates. Intrusion did not increase multiple paternity, though multiple paternity was significantly greater in the first trial when the males were virgins compared to the second trial. Since virgin male mice are highly infanticidal, this finding is consistent with the infanticide avoidance hypothesis. We also found that multiple paternity was higher when competing males showed small differences in their amount of scent marking, suggesting that females reduce MMM when they can detect differences in males' quality. Finally, multiple paternity was associated with increased litter size but only in the intrusion treatment, which suggests that the effect of multiple paternity on offspring number is dependent on male-male interactions.

Social learning in Cartilaginous fish (stingrays Potamotrygon falkneri).

Social learning is considered one of the hallmarks of cognition. Observers learn from demonstrators that a particular behavior pattern leads to a specific consequence or outcome, which may be either positive or negative. In the last few years, social learning has been studied in a variety of taxa including birds and bony fish. To date, there are few studies demonstrating learning processes in cartilaginous fish. Our study shows that the cartilaginous fish freshwater stingrays (Potamotrygon falkneri) are capable of social learning and isolates the processes involved. Using a task that required animals to learn to remove a food reward from a tube, we found that observers needed significantly (P < 0.01) fewer trials to learn to extract the reward than demonstrators. Furthermore, observers immediately showed a significantly (P < 0.05) higher frequency of the most efficient "suck and undulation" strategy exhibited by the experienced demonstrators, suggesting imitation. Shedding light on social learning processes in cartilaginous fish advances the systematic comparison of cognition between aquatic and terrestrial vertebrates and helps unravel the evolutionary origins of social cognition.

Scent marking increases male reproductive success in wild house mice.

Scent marking is often assumed to be a secondary sexual trait that increases males' mating and reproductive success, although direct evidence for this hypothesis is lacking. We conducted a study with wild-derived house mice, Mus musculus musculus, to test whether scent marking increases males' reproductive success when females can freely choose between two territorial males. We also experimentally manipulated males' competitive scent marking by exchanging scent-marked tiles between the neighbouring males' territories (intrusion treatment) or relocating males' tiles within their own territory (control). Experimental animals were tested twice and we examined whether individual males were consistent in their marking. We found that males marked more in the intrusion treatment than controls and more at shared territorial borders than elsewhere. We found high day-to-day variation in most individuals' scent marking, and yet the sum of individuals' scent marking was consistent over time and across different social conditions. Genetic paternity analyses revealed that males' scent marking significantly increased their reproductive success in both the intrusion treatment and the controls. Surprisingly, however, female social preference was not positively correlated with male scent marking. These results provide direct evidence that scent marking increases males' reproductive success when females can choose their mates, even though it did not increase females' social preferences.