Age and brood defence in male CRL:NMRI BR laboratory mice, Mus musculus domesticus

According to Lack's principle, older mice should invest more in their offspring than younger ones. I tested this principle with pairs of CRL:NMRI BR mice protecting their young against an intruder, an unfamiliar same-stock male or female. The intruder was presented within a small wire-mesh cage in an extension, a cage the same size as the pair's home cage. The dam, her mate and the young in the nest were present in all tests. Although both parents had full access to the intruder, only the male interacted with it. Young breeding pairs and young intruders were 6 months old, the old pairs and old intruders 12 months. Each breeding pair was tested with both young and old male intruders. Older males defended their pups more vigorously than younger ones. The old males showed a higher preference to stay near (to interact with) the opponent; they also showed more tail rattling and biting attempts than the young ones. This indicates that older males take greater risks in defending their offspring than younger males. Older intruders also elicited a stronger brood defence in older males and a weaker response in younger ones.     

Factors affecting the recognition of territory boundaries by mice (Mus musculus)

Male mice of the LACA strain and from a wild stock were allowed to form territories in 180-cm² enclosures. The clues by which they recognized the position of the territory boundaries were investigated by moving various landmarks or reference objects. The information used was found to be primarily visual, close objects taking precedence over distant ones. Olfactory clues were also used but only when they did not conflict with the visual ones. Cover was found to be necessary for territory formation, but not for maintenance, and the size of the territory apparently influenced the aggressiveness of the mouse holding it.     

Control of moulting in the house cricket, Acheta domesticus

Last-instar Acheta domesticus moulted 7–8 days after the beginning of feeding, following ecdysis, or following starvation. Two full days of feeding were required for commitment to moult, and the minimal food consumption was estimated at 80–110 mg. All day-0 larvae weighing 200 mg, that achieved a critical weight of 280–300 mg after 48 hr of feeding, moulted. Two kinds of experiments indicated that an approximate 50% increase in wet-weight gain was required for a commitment to moult, which occurred at the end of the second day of feeding. Neck ligatures indicated that a head factor, presumably prothoracicotropic hormone, (PTTH), was released during the third day after the beginning of feeding provided the critical weight was achieved. Neither PTTH release nor ecdysis appeared to be under photoperiodic control in Acheta.     

Conditions for landmark-based navigation in the house mouse, Mus musculus

I investigated whether mice, after learning to home by relying on visual extra-arena landmarks, still required instantaneous access to such cues for successful navigation. Two groups of lactating mice were trained to retrieve their pups from the centre of a circular arena back to their peripheral nest. On test trials, mice from one group were allowed to view distal visual cues while moving from the nest towards the centre, and mice from the other group were allowed to view distal visual cues when homing from the centre towards the nest. The results indicate that viewing the visual cues when homing is necessary for landmark-based navigation.     

Ethological isolation between local populations of house mice (Mus musculus) based on olfaction

Some rodent populations are composed of demes which remain reproductively isolated within the major population. Territoriality has been advanced as a possible isolating mechanism. This research investigated the possible role of olfaction in the isolation of feral house mouse (Mus musculus) demes. When given a choice, male and female mice spent more time with the air-transported odours of members of their own deme than with those of neighbouring deme members. Tests with a fresh-air control showed that mice avoided the odours of members of an adjacent deme. In addition, more time was spent with urine and faeces odours of members of a mouse's own group than with those of the members of an adjacent deme. The production and detection of odorous substances may contribute to the autonomy and relative reproductive isolation of some local populations of mice.     

Physiological regulation of long-term oviposition in the house cricket, Acheta domesticus

In house crickets [Acheta domesticus (L.)] a single mating early in adult life sufficed to induce egg laying for the duration of the life of a female. Female house crickets mated readily shortly after adult emergence but oviposition did not commence until about 12–14 days after emergence, even though females matured eggs by 7 days. The egg-laying factor associated with mating remained active during prolonged periods of substrate deprivation during which the female did not oviposit. If the spermatophore was removed prematurely shortly after a mating, the long-term, egg-laying response was truncated and was correlated with a dramatic decline in the fertility of eggs which were oviposited. The egg-laying stimulus appeared to act in the spermatheca, apparently through neural means, since denervation of the spermatheca abolished mating-induced oviposition. These results indicate that the oviposition factor found in the testes is able to act for long periods of time and has to be present continually in order to be effective. Furthermore, the long-term oviposition stimulus in the house cricket may be different from prostaglandin E2 which induces a prompt ovipositional response.     

Ghrelin's quick inhibition of androgen-dependent behaviors of male house mice (Mus musculus)

Ghrelin is a peptide hormone released by the stomach that stimulates hunger. Ghrelin also suppresses reproductive physiology by inhibiting the HPG axis. However, to our knowledge, our results are the first to demonstrate ghrelin's quick suppression of sex-hormone-regulated behaviors. In experiment 1, 2 orexigenic i.p. ghrelin injections (0.165 mg/kg and 0.33 mg/kg) suppressed male courtship behavior (ultrasonic calling to a female) and intermale aggression (latency to attack a stimulus male) 20 min following administration. Experiment 2 (examining only the 0.33 mg/kg dose ) replicated ghrelin's suppression of ultrasonic calling and intermale aggression; however, a third behavior, preference for volatile female odors (20 min following administration), was not significantly inhibited. In experiment 2, ghrelin treatment did not affect general locomotor activity (distance traveled 20 min following injection) or seminal vesicle weight (measured 5 days after completing ghrelin injections). We hypothesize that ghrelin's quick suppression of male aggression and ultrasonic mating calls was mediated through its effects on the brain (rather than indirectly through inhibition of the HPG axis).     

Coevolution of Cryptosporidium tyzzeri and the house mouse (Mus musculus)

Two house mouse subspecies occur in Europe, eastern and northern Mus musculus musculus (Mmm) and western and southern Mus musculus domesticus (Mmd). A secondary hybrid zone occurs where their ranges meet, running from Scandinavia to the Black Sea. In this paper, we tested a hypothesis that the apicomplexan protozoan species Cryptosporidium tyzzeri has coevolved with the house mouse. More specifically, we assessed to what extent the evolution of this parasite mirrors divergence of the two subspecies. In order to test this hypothesis, we analysed sequence variation at five genes (ssrRNA, Cryptosporidium oocyst wall protein (COWP), thrombospondin-related adhesive protein of Cryptosporidium 1 (TRAP-C1), actin and gp60) in C. tyzzeri isolates from Mmd and Mmm sampled along a transect across the hybrid zone from the Czech Republic to Germany. Mmd samples were supplemented with mice from New Zealand. We found two distinct isolates of C. tyzzeri, each occurring exclusively in one of the mouse subspecies (C. tyzzeri-Mmm and C. tyzzeri-Mmd). In addition to genetic differentiation, oocysts of the C. tyzzeri-Mmd subtype (mean: 4.24 × 3.69 μm) were significantly smaller than oocysts of C. tyzzeri-Mmm (mean: 4.49 × 3.90 μm). Mmm and Mmd were susceptible to experimental infection with both C. tyzzeri subtypes; however, the subtypes were not infective for the rodent species Meriones unguiculatus, Mastomys coucha, Apodemus flavicollis or Cavia porcellus. Overall, our results support the hypothesis that C. tyzzeri is coevolving with Mmm and Mmd.     

Effect of intranasal irrigation with zinc sulphate on male-induced oestrus in the wild mouse, Mus musculus domesticus

Adult males of the subtropical house sparrow (Passer domesticus) were subjected to continuous darkness (DD) or short days (8L:16D) after photostimulation (15L:9D) for 30 days. One group was retained on the long day (15L:9D) schedule. Another two groups of photosensitive birds were placed under DD or 8L:16D. The photostimulated birds under DD or 8L:16D showed testicular regression and the rate of regression was similar in both the treatments. The photosensitive birds, on the other hand, did not show any initiation in testicular growth and development in either of the treatments. Long day birds (15L:9D) maintained enlarged testes without regression (the onset of photorefractoriness) during the treatment period. These results conform with the external coincidence model, but could also be explained by a modified internal coincidence model.     

The effect of temperature on energy distribution during the last-larval stadium of the female house cricket, Acheta domesticus

The distribution of energy during the last stadium of the house cricket at two temperatures was the main theme of this study. Food consumption, growth, and oxygen consumption were greater in the first half of the stadium at both 25 and 35°C. An RQ > 1 indicated the conversion of carbohydrates to lipids during the first half of the instar at both temperatures. The duration of the stadium increased from 6 days at 35°C to 14 days at 25°C. The same maximal weight, protein content and lipid content were attained at both 25 and 35°C. A weight loss (mostly in stored lipids) after the midstadium peak weight was greater at the lower temperature. The absorption efficiency and the production of metabolic wastes were not affected by temperature, but the metabolic efficiency was much higher at 35 than at 25°C during the first half as well as the latter half of the stadium. Although during the first half of the stadium more energy was ingested, absorbed, and made available for growth at 25 than at 35°C, only slightly more growth occurred at 25°C. During the last half of the stadium less energy was ingested at 25 than at 35°C, and much more growth occurred at 35°C because of the even greater heat loss at 25 than at 35°C. Therefore at a lower temperature cricket larvae eat slightly more and reach the same maximal weight as at a higher temperature, but they end up smaller because they waste more energy during the extended duration of the stadium at the lower temperature.     

Serotonin has kinin-like activity in stimulating secretion by Malpighian tubules of the house cricket Acheta domesticus

Serotonin stimulates secretion by Malpighian tubules (MT) of a number of insects, and functions as a diuretic hormone in Rhodnius prolixus and in larval Aedes aegypti. Serotonin is here shown to be a potent stimulant of secretion by MT of the house cricket, Acheta domesticus, with an apparent EC₅₀ of 9.4 nmol L⁻¹, although its diuretic activity is just 25% of the maximum achievable with either the native CRF-related peptide, Achdo-DH, or a crude extract of the corpora cardiaca. In this respect, the diuretic activity of serotonin is similar to that of the cricket kinin Achdo-KI, and when tested together their actions are not additive, which suggests they target the same transport process. Consistent with this suggestion, the activity of serotonin is chloride-dependent and is associated with a non-selective stimulation of NaCl and KCl transport. In common with Achdo-KI, serotonin has no effect on cAMP production by isolated MT, and both act synergistically with exogenous 8bromo-cAMP in stimulating fluid secretion, most likely by promoting the release of Ca²⁺ from intracellular stores. A number of serotonin agonists and antagonists were tested to determine the pharmacological profile of receptors on cricket MT. The results are consistent with the diuretic activity of serotonin being mediated through a 5-HT₂-like receptor.     

Immune investment impairs growth, female reproduction and survival in the house cricket, Acheta domesticus

We investigated whether an immune response is associated with growth, female reproduction and survival costs in the house cricket. Using different intensities of challenge immune (implantation of one piece of nylon (1N) and two nylons (2N), with their respective sham-challenge and control groups) with body size and exoskeleton thickness as response variables, growth costs were determined for both sexes. A similar methodology was followed for reproduction costs, in which egg number and size, and female survival were measured as response variables. It was also determined whether mated and virgin females showed different immune responses. Body size decreased with immune challenge but only in the 2N treatment. Exoskeleton thickness increased in both sham-challenge groups and the 1N group but decreased in the 2N group. Egg number decreased more in the sham-challenge groups followed by the 1N and 2N groups. The 2N group showed the largest egg size at the end of the experiment. In these females, 2N group died first followed by the 1N, two nylon sham and one nylon sham groups. Finally, mated females showed a lower immune response than virgin females. These results are consistent with ecological immunity theory. The discovery of exoskeleton-related costs of immunity and injury may have important implications for experimental design in studies of the cost of immunity.     

Relationships of maternal nesting to thermoregulatory nesting in house mice (Mus musculus) at warm and cold temperatures

Thermoregulatory and maternal nesting in Mus musculus (indexed as weight of cotton pulled into the cage) was measured at 5 C and 22 C on mice representing lines from a bidirectional selection experiment for nest size at room temperature. The effects of both selection and temperature were significant across the entire experiment. Nesting on the day of parturition correlated highly with thermoregulatory nesting, and with the number of offspring that survived to weaning, indicating a common genetic basis for maternal and thermoregulatory nesting and a direct correlation of these traits with Darwinian fitness. Amount of cotton used increased soon after mating and remained high with a large amount of variability until about 10 days after parturition, and then decreased sharply. The pattern of changes in nest size during pregnancy resembled changes in progesterone levels reported previously in the literature for mice, and contrasted with models of a smooth symmetric curve peaking at parturition.     

Relation of blood composition to age in the larval female house cricket, Acheta domesticus

The blood volume, osmolality, and sugar concentration increase; the blood protein and lipid concentration decrease; and the blood ions and NPS concentration do not change during apolysis from the 7th to 8th instar of larval Acheta domesticus. The patterns of change in all blood constituents are basically identical in both of the last two larval instars. Blood volume increase is directly related to growth, but not directly to total body water. Blood protein concentration increases in exact relation to growth, resulting in a doubling of concentration by midinstar and a small decrease over the last 2 to 3 days. The concentration of clottable protein remains constant; the soluble protein concentration increase probably providing cuticular proteins prior to and following ecdysis. Blood lipid concentration increases steadily throughout both instars, even during the non-feeding phase. Total blood carbohydrate concentration decreases greatly in the first 2 days of an instar, then remains relatively constant for the remainder of the instar. Blood trehalose concentration is 85% of the total carbohydrate concentration throughout the instar, but drops to 65% with a corresponding increase in ‘other sugars’ with the onset of apolysis on the last day. Growth demands probably exceed dietary supply of amino acids resulting in a 50% decrease in NPS concentration in the first half of the instar, then NPS concentration increases in spite of a declining feeding rate because growth demands cease. Within the normal blood ion lability range, the principle blood ions, sodium and chloride, vary in an inverse proportion to NPS and sugar concentration at least in the first two-thirds of the instar. Thus blood osmolality is constant except for an unexplained drop in the last 2 days of an instar.