Free female mate choice in house mice affects reproductive success and offspring viability and performance

We tested a critical assumption of sexual dialectics theory (Gowaty 1997, Feminism and Evolutionary Biology, Chapman & Hall) using house mice, Mus musculus. We asked if female house mice accrue viability benefits for their offspring when they mate with males they prefer versus with males they do not prefer. Our experiment was designed to eliminate or control other mechanisms of reproductive competition besides female mate choice. After allowing females to discriminate behaviourally between two males, which were at random with respect to phenotypic variation discriminating females were paired with preferred (P) or nonpreferred (NP) males. We then tested whether females mating with males they preferred had offspring of higher viability than females mating with nonpreferred males. In pairwise comparisons, we tested for differences in offspring performance in dominance contests and in nest-building skill. At weaning, we exposed half of the pups to cold stress. We tested progeny performance and viability in the laboratory or in outdoor field enclosures. In comparison to P females, NP females produced significantly fewer litters. Sons from P matings were socially dominant to sons from NP matings. Adult offspring from P matings built better nests than those from NP matings. In field enclosures significantly fewer NP than P offspring survived to 60 days after introduction. Male and female progeny from P matings established larger home ranges and constructed better nests than progeny from NP matings. This is the first demonstration of progeny viability differences for females allowed to express mate preferences between males presented to them at random. Copyright 2000 The Association for the Study of Animal Behaviour.     

Genetic effect of mottled locus on reproduction and preweaning growth in laboratory mice

Summary An experiment was conducted to study the maternal and fetal effects of the sex-linked gene tortoise on litter size, birth weight, body weight from birth to 30-day of age, and mortality in normal (N) and mutant (M) mice (Mus musculus). The experiment involved two mating types: (1) N x N (dam x sire) which produced normal male and normal female offspring and (2) M X N which produced mutant males that died in utero, mutant females and normal male and female offspring. Comparison 1 consisted of all phenotypically normal male and female offspring from both N X N and M X N mating types born in 2 parities. The data supports the hypothesis that the tortoise gene, when present in the dam, did not significantly affect the body weight of normal progeny prior to 18 days old. There is also evidence for a negative maternal effect of the tortoise gene on body weight from 21 to 30 days of age postpartum. Mating type X parity interaction was not significant prior to 9 day postpartum. Sex of mice did not influence body weight of siblings prior to 18 day old, but males were heavier than females there-after. Normal and mutant females born in six parities from the M X N mating type constituted Comparison 2. The birth weight of the offspring in Comparison 2 was not significantly influenced by the presence of the tortoise gene. All other body weight measurements, however, were lower for mutant females when compared to normal females. Parity affected all body weight measurements in both comparisons. Mortality rate of the offspring was not influenced by parental mating type or parity, but sex differences were observed. Mutant females had higher mortality than normal sisters. This study provides evidence that the mottled locus in the tortoise dam and progeny influences growth and survival.Reference to a company and/or product named by the USDA is only for purposes of information and does not imply approval or recommendation of the product to the exclusion of others     

Colour Polymorphism and Alternative Breeding Strategies: Effects of Parent’s Colour Morph on Fitness Traits in the Common Wall Lizard

Colour polymorphism (CP) is widespread in animals, but mechanisms underlying morph evolution and maintenance are not completely resolved. In reptiles, CP is often genetically based and associated with alternative behavioural strategies, mainly in males for most cases. However, female colour morphs also display alternative reproductive strategies associated with behavioural and physiological traits, which may contribute to maintain CP in the population. Both sexes of the common wall lizard (Podarcis muralis) show three pure colour morphs, white, yellow and red. Here, we looked for the effects of male and female colour morphs on fitness traits of captive-breeding pairs. All yellow-throated females laid clutches of many small eggs and produced many light offspring, behaving as r-strategists, whereas white-throated females laid clutches of few large eggs and produced few heavy offspring, behaving as K-strategists. Red-throated females adopted a conditional Kr-strategy depending on their size/age. These basic female strategies were modulated in relation to mate morph: white females had the best fitness gain in terms of viable offspring when mated to red males; mating between yellow morphs yielded a greater breeding success than all other morph crosses, but also lighter offspring; finally, red females produced heavy progeny when paired with red or white males, and light offspring in pair with yellow males. Thus, correlation between CP and traits relevant to fitness combined with non-random mating, either assortative or disassortative, could increase the potential for CP to contribute to divergent evolution in the common wall lizard.     

Plasticity in male mating behavior modulates female life history in fruit flies

In many species, intense male-male competition for the opportunity to sire offspring has led to the evolution of selfish reproductive traits that are harmful to the females they mate with. In the fruit fly, Drosophila melanogaster, males modulate their reproductive behavior based on the perceived intensity of competition in their premating environment. Specifically, males housed with other males subsequently transfer a larger ejaculate during a longer mating compared to males housed alone. Although the potential fitness benefits to males from such plasticity are clear, its effects on females are mostly unknown. Hence, we tested the long-term consequences to females from mating with males with distinct social experiences. First, we verified that competitive experience influences male mating behavior and found that males housed with rivals subsequently have shorter mating latencies and longer mating durations. Then, we exposed females every other day for 20 days to males that were either housed alone or with rivals, and subsequently measured their fitness. We found that females mated to males housed with rivals produce more offspring early in life but fewer offspring later in life and have shorter lifespans but similar intrinsic population growth rates. These results indicate that plasticity in male mating behavior can influence female life histories by altering females’ relative allocation to early versus late investment in reproduction and survival.     

Strong male/male competition allows for nonchoosy females: high levels of polygynandry in a territorial frog with paternal care

Our knowledge about genetic mating systems and the underlying causes for and consequences of variation in reproductive success has substantially improved in recent years. When linked to longitudinal population studies, cross-generational pedigrees across wild populations can help answer a wide suite of questions in ecology and evolutionary biology. We used microsatellite markers and exhaustive sampling of two successive adult generations to obtain population-wide estimates of individual reproductive output of males and females in a natural population of the Neotropical frog Allobates femoralis (Aromobatidae), a pan-Amazonian species that features prolonged iteroparous breeding, male territoriality and male parental care. Parentage analysis revealed a polygynandrous mating system in which high proportions of males (35.5%) and females (56.0%) produced progeny that survived until adulthood. Despite contrasting reproductive strategies, successfully reproducing males and females had similar numbers of mating partners that sired the adult progeny (both sexes: median 2; range 1-6); the numbers of their offspring that reached adulthood were also similar (both sexes: median 2; range 1-8). Measures of reproductive skew indicate selection on males only for their opportunity to breed. Reproductive success was significantly higher in territorial than in nonterritorial males, but unrelated to territory size in males or to body size in both sexes. We hypothesize that female polyandry in this species has evolved because of enhanced offspring survival when paternal care is allocated to multiple partners.     

The sexual function of mature rat males after prenatal modulation of cholinergic system

The data obtained have shown that prenatal exposure of pregnant rat females of 9-19-day pregnancy to N-cholinolytics as compared to M-cholinolytics produce long-term behavioural changes in pubescent rat progeny. Pubescent rat progeny had low dynamics of gaining sexual experience and decreased sexual activity with equal disturbance of motivation and coitus. The number of males with absence of sexual activity was above that of the control group. We suggest that sexual dysfunction of offspring adulthood was provoked by introduction of ganglerone (N-cholinolytic) which had been injected on 9-11 and 12-14 days of gestation, and metamyzil (M-cholinolytic) injected on 9-11 days of gestation. Apparently, regulation of neuronal mechanisms for sexual function is disturbed as a consequence of lasting change in neurotransmitter activity. It is suggested that dopaminergic activity in brain limbic structures was affected the most. The significant decrease in blood testosterone values has also been elucidated.     

Evidence against an essential role of endogenous brain dopamine in methamphetamine-induced dopaminergic neurotoxicity

The present studies examined the role of endogenous dopamine (DA) in methamphetamine (METH)-induced dopaminergic neurotoxicity while controlling for temperature-related neuroprotective effects of the test compounds, reserpine and alpha-methyl-p-tyrosine (AMPT). To determine if the vesicular pool of DA was essential for the expression of METH-induced DA neurotoxicity, reserpine (3 mg/kg, given iintraperitoneally 24-26 h prior to METH) was given prior to a toxic dose regimen of METH. Despite severe striatal DA deficits during the period of METH exposure, mice treated with reserpine prior to METH developed long-term reductions in striatal DA axonal markers, suggesting that vesicular DA stores were not crucial for the development of METH neurotoxicity, but leaving open the possibility that cytoplasmic DA might be involved. To evaluate this possibility, cytoplasmic DA stores were depleted with AMPT prior to METH administration. When this study was carried out at 28 degrees C, complete neuroprotection was observed, likely due to lingering effects on core temperature because when the same study was repeated at 33 degrees C (to eliminate AMPT's hypothermic effect in METH-treated animals), the previously observed neuroprotection was no longer evident. In the third and final set of experiments, mice were pretreated with a combination of reserpine and AMPT, to deplete both vesicular and cytoplasmic DA pools, and to reduce striatal DA levels to negligible values during the period of METH administration (< 0.05%). When core temperature differences were eliminated by raising ambient temperature, METH-induced DA neurotoxic changes were evident in mice pretreated with reserpine and AMPT. Collectively, these findings bring into question the view that endogenous DA plays an essential role in METH-induced DA neurotoxicity.     

Effects of sympathetic denervation on follicular distribution,oestradiol and progesterone serum levels in prepubertal hemi-ovariectomized female guinea pig

The aim of this study was to determine the effects of maternal undernutrition during pregnancy on adult reproductive function in male and female offspring. Groups of ewes were fed rations providing either 100% (High, H) or 50% (Low, L) of estimated metabolisable energy (ME) requirements for pregnancy, from mating until day 95 of gestation, and thereafter were conventionally managed. At 20 months of age, LH and FSH profiles, and LH responses to exogenous GnRH were measured in male and female offspring and, in males, testicular responses to exogenous LH (as measured by testosterone concentrations) were also measured. Undernutrition had no effect on the mean birth weights of lambs of either sex, or on testicular size in male animals at either 6 weeks or 20 months of age. L males exhibited significantly higher FSH concentrations than H males (P < 0.05) but there were no differences with treatment in FSH profiles in females, basal LH profiles or gonadotrophin responses to GnRH in offspring of either sex, and no difference in basal testosterone concentrations or in the testosterone response to exogenous LH administration in males. Semen quality at 20 months of age was unaffected by pre-natal undernutrition but ovulation rate was significantly reduced in L compared to H female offspring (P < 0.05). It is concluded that pre-natal undernutrition had no effect on male reproductive development and adult function, but reduced ovulation rate in female progeny. This effect was not associated with a change in gonadotrophin profiles or pituitary responsiveness.     

Effects of paternal ethylene dibromide exposure on F1 generation behavior in the rat

The effects of ethylene dibromide (EDB) exposure to the male rat were studied through behavioral assessments of their F1 progeny. Exposed males were bred with untreated female rats at 4 or 9 weeks after 5 daily EDB treatments. Behavioral assessment of motor reflexes and motor coordination were examined up to 21 days of age. Significant differences in the development of motor coordination and motor activity were observed in the F1 progeny of EDB-exposed males. These results support the evidence of EDB genotoxicity and further demonstrates the utility of behavioral end-points of the offspring as a sensitive means of assessing paternal reproductive risk.     

根田鼠母体捕食应激对其子代运动及探究行为的作用

本文研究了根田鼠母体捕食应激对其子代运动及探究行为的作用。母体自妊娠中期至分娩期间,每天被短暂且重复地暴露给艾鼬。分娩后,对母体及其子代正常饲养。在子代性成熟后,分别测定其运动和探究行为。母体捕食应激显著降低子代的运动时间和频率。在探究行为中,母体捕食应激子代的探究潜伏期和探究时间均显著大于对照子代;其次,母体捕食应激雌性子代的探究次数显著小于对照。另外,个体的运动水平以及探究潜伏期和探究次数均存在性别差异。本研究结果表明,田鼠类母体捕食应激对其子代运动和探究行为有显著的抑制作用,由此可能对子代适合度,乃至种群波动产生负效应。     

Paternal effects associated with melanism in Harmonia axyridis (Coleoptera: Coccinellidae): mating sequence asymmetries and interactions with age‐specific maternal effects

1. For this study a cohort of melanic Harmonia axyridis males homozygous for the spectabilis allele was produced. These were used to produce four kinds of twice‐mated females, comprising all four permutations of melanic and non‐melanic (succinic) males. A series of 12 larvae were then reared from the first and 10th clutches of each female to compare progeny developmental phenotypes. 2. There were no effects of mating treatment on overall female reproductive performance (preoviposition period, 20‐day fecundity, or egg fertility). 3. Age‐specific maternal effects were evident in progeny developmental phenotypes; larvae of 10th clutches developed more slowly, pupation was shorter, and adults emerged at heavier weights. 4. Paternal effects were superimposed on maternal effects and affected progeny independent of their paternity; melanic males induced slower larval development and slower pupation, but only in 10th clutches and only when they mated second. 5. There was a significant three‐way interaction between male mating treatment, clutch number and progeny phenotype, indicating that progeny developmental responses to (mixed) paternal effects varied depending on their own phenotype and the time elapsed since their mother's last mating. 6. Melanic males mating second obtained a P2 advantage over succinic males, which increased from first to 10th clutch, but the reverse was not true when succinic males mated second. Thus, polyandry in H. axyridis facilitates both genetic and epigenetic competition among males while simultaneously enabling the sharing of predominant paternal effects among the progeny of different fathers.     

Effects of multiple matings on reproductive fitness of male and female Diaeretiella rapae

Mating frequency and the amount of sperm transferred during mating have important consequences on progeny sex ratio and fitness of haplodiploid insects. Production of female offspring may be limited by the availability of sperm for fertilizing eggs. This study examined multiple mating and its effect on fitness of the cabbage aphid parasitoid Diaeretiella rapae McIntosh (Hymenoptera: Aphidiidae). Female D. rapae mated once, whereas males mated with on average more than three females in a single day. The minimum time lag between two consecutive matings by a male was 3 min, and the maximum number of matings a male achieved in a day was eight. Sperm depletion occurred as a consequence of multiple mating in D. rapae. The number of daughters produced by females that mated with multiple‐mated males was negatively correlated with the number of matings achieved by these males. Similarly, the proportion of female progeny decreased in females that mated with males that had already mated three times. Although the proportion of female progeny resulting from multiple mating decreased, the decrease was quicker when the mating occurred on the same day than when the matings occurred once per day over several days. Mating success of males initially increased after the first mating, but then males became ‘exhausted’ in later matings; their mating success decreased with the number of prior matings. The fertility of females was affected by mating with multiple‐mated males. The study suggests that male mating history affects the fitness of male and female D. rapae.     

Improving male mating competitiveness and survival in the field for medfly,Ceratitis capitata (Diptera: Tephritidae) SIT programs

The success of the sterile insect technique (SIT) depends critically upon mating between released sterilized males and wild females. In Hawaii, improvements in the efficiency of sterile males were attempted on two separate fronts – mating enhancement and survival improvement. In the former, two methods have been investigated – selective breeding and aromatherapy. In the latter, flies which survived in field cages for several days were selected and bred to produce progeny with enhanced survival ability compared to control flies. Regarding mating selection, standard laboratory-reared males that successfully mated with wild females in field cages were allowed to breed. F1 offspring were inbred, then the selection procedure was repeated for four additional cycles. In the aromatherapy procedure, laboratory-reared males were exposed to ginger root oil for several hours 1 day prior to testing in field cages. Compared to controls, the selected flies improved the mating competitiveness of male flies ca. 3-fold, irradiation reduced this increase to ca. 2.5-fold. Exposing the selected, hybrid strain raised the fitness of the lab males to ca. 9-fold that of wild males. In the ongoing survival selection study, we have obtained lines in which the selected males survived ca. 2-fold better than laboratory control males over several days in an outdoor field cage, with food and water provided. The goal is to combine the traits of higher survival and mating ability into a single strain for SIT release.     

Free mutual mate preferences in house mice affect reproductive success and offspring performance

When social constraints on the expression of mate preferences are absent, variation in offspring viability is predicted to favour females and males that display mate preferences. Earlier studies showed that female and male house mice, Mus domesticus, tested individually and mated with preferred (P) partners had higher reproductive success and better progeny performance than individuals mated with nonpreferred (NP) partners. Here we tested the effects of mutual mate preferences on reproductive success, offspring viability and performance. We conducted mate preference tests and created four types of reproductive pairings. One involved females and males that preferred each other (P-P); the second type had females that preferred the male but the male did not prefer the female (P-NP); the third had females that did not prefer the male but the male did prefer the female (NP-P). The last set consisted of females and males that did not prefer each other (NP-NP). We measured components of fitness for breeders (reproductive success) and offspring viability (birth-to-weaning viability and weight variation) as well as measures of offspring performance. There were no statistical differences in reproductive success of breeders or offspring viability and quality (weight variation) among the four types of pairings. There were, however, consistent differences between P-P versus NP-NP matings. The number of pups weaned, time to first litter, birth-to-weaning viability, pup body weight at birth and weaning, and the growth rates for pups of both sexes were consistently greater for progeny from P-P matings than NP-NP matings. Significant differences occurred among the four mating types in dominance of sons during aggression trials, nest construction and predator avoidance. Progeny from P-P matings displayed behaviour associated with higher fitness more often than progeny from NP-NP matings. These data show that breeders produce more highly competent progeny, most likely to survive, when social constraints on the expression of mate preferences in both sexes are relaxed.Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

Effects of ω3 Polyunsaturated Fatty Acids on Growth and Tissue Fatty Acid Compositions of Maternal Rats and Their Progeny

The effects of ω3 polyunsaturated fatty acids [PUFA; mainly eicosapentaenoic acid (20: 5, ω3) and docosahexaenoic acid (22:6, ω3)] on the growth, tissue weights and fatty acid compositions of tissue total lipids in female rats and their progeny were investigated. Female rats of the Wistar strain, weighing 77~94g, were fed a 25% casein diet containing 5% of either corn oil (control), sardine oil or PUFA ethyl ester for 8 ~ 9 weeks prior to mating, and during gestation and lactation, and then for a further 2 weeks. The progeny were weaned to the maternal diet and then the latter was administered for a further 2 weeks. Dietary changes in the body weights of the dams were not generally seen, but the body weights at birth and growth of the offspring from the females supplied with the PUFA diet were inferior compared to those of the other groups. The fertility did not differ among the dietary groups. The weights of several tissues in the dams and the progeny increased in proportion to their body weights but not that of the progeny brain, which remained ' almost unchanged by the dietary fats. As to the fatty acid compositions of total lipids in the tissues, on the whole, decreased levels of ωβ fatty acids and increased percentages of ω3 fatty acids were found in the sardine and PUFA groups, the changes being greater in the PUFA group than in the sardine one. Such findings due to the feeding of PUFA were more remarkable in the progeny compared with in the dams. Eicosatrienoic acid (20: 3, ω9) was almost completely undetectable in the tissue total lipids of all the dietary groups.     

Mating, cross-mating and related behaviours of Neoseiulus californicus and Neoseiulus fallacis (Acari: Phytoseiidae)

The pairings of Neoseiulus californicus (McGregor) and Neoseiulus fallacis (Garman) from western North America were monitored for tending by adult males, males in the mating position and oviposition and the activity of female deutonymphs and adults. The N. fallacis × N. californicus (♂ × ♀) tests had fewer males tending the deutonymphs but more in the mating position with new females than the reciprocal test. Afterwards, most of the females appeared gravid and approximately 20% produced an egg. Some eggs did not hatch but others became adult males, which mated with their mothers, but no eggs were produced. F1 males tended and mated with new N. fallacis females which had normal offspring. When held with new N. californicus females, F1 males tended the deutonymphs but were not seen mating and no eggs were laid. The pairings of N. californicus× N. fallacis had more males tending, less in the mating position and the females appeared non-gravid and produced no eggs. When same-species males were added to females held with F1 males for 15–20 days, normal levels and sexes of the progeny were produced. The female and male adults of N. fallacis were more active (ambulatory) than those of N. californicus. In within-species tests, the males had a high activity except while tending and mating, the female deutonymphs were inactive and the just mated females were more active than the ovipositing females. The timing of the tending and mating differed in the cross-pairings. Overall, these and other life-history data show that these two mites are distinct species, but that their males are promiscuous in tending and mating. This revised version was published online in November 2006 with corrections to the Cover Date.     

Polyandry restores female fertility and paternal effects diminished by inbreeding in Hippodamia convergens

1. The fertility restoration hypothesis posits that polyandry can evolve when female fertility is reduced by matings with related males, but restored by matings with unrelated ones. 2. Using a promiscuous ladybird, this hypothesis was tested by mating mature, virgin females twice with sib and non‐sib males in all four permutations and observing female fertility. The development of progeny from the first and 10th clutches was also followed to test for differences in paternal effects. 3. Mating treatment did not affect fecundity, but egg viability was reduced by sib matings, and restored by non‐sib matings, regardless of mating sequence. In addition, negative paternal effects of sib matings on progeny (lower survival) were compensated by non‐sib matings. 4. The survival of offspring in first clutches was sensitive to the paternal mating sequence and was higher if a sibling male was preceded by a non‐sib male, compared with the reverse, consistent with a time lag in response to male epigenetic signals. Offspring survival did not differ between these two treatments in the 10th clutch, suggesting a blending of paternal effects over time. 5. The results are indicative of interactions between the paternal effects contributed by different males, and between paternal and maternal effects, the latter causing faster development in later clutches. 6. Thus, the reproductive benefits of polyandry for H. convergens females are potentially both genetic and epigenetic, as both egg fertility and beneficial paternal effects were diminished by sib matings, but restored by matings with unrelated males.     

The pharmacokinetic properties of methamphetamine in rats with previous repeated exposure to methamphetamine: the differences between Long-Evans and Wistar rats.

Repeated treatment with methamphetamine (METH) causes long-term behavioral changes, so-called behavioral sensitization (BS), in humans as well as experimental animals. However, there are no reports as to whether repeated METH treatment can establish BS in stress-sensitive Long-Evans (LE) rats. Thus, we investigated the effect of repeated METH treatment (5 mg/kg x 5 days) on the establishment of BS in LE rats. Wistar (WIS) rats were used as a reference. In LE rats, repeated METH treatment failed to cause BS although it did enhance METH-induced hyperlocomotion in WIS rats. The levels of METH in brain dialysate and the ratio of the area under the concentration-time curve area in plasma to that in brain dialysate was increased in repeated METH-treated WIS rats as reported previously, but not in repeated METH-treated LE rats. METH increases plasma corticosterone (CORT) in both strains. However, the intensity of increment of CORT by repeated METH was lower in LE rats than that in WIS rats. Repeated METH treatment decreased the expression of METH-transposable and CORT-sensitive transporter, organic cation transporter 3 (OCT3), in the brain of WIS rats. However, the intensity of the decrement of OCT3 with repeated METH treatment was similar between both strains. Taken together, these results suggest that the lack of establishment of BS in LE rats might have been caused by the unchanged brain penetration of METH after repeated METH administration, and that the differential CORT response to METH is an important strain difference.     

Attenuation of Cocaine and Methamphetamine Neurotoxicity by Coenzyme Q10

The neurotoxic effects of cocaine and methamphetamine (METH) were studied in mice brain with a primary objective to determine the neuroprotective potential of coenzyme Q₁₀ (CoQ₁₀) in drug addiction. Repeated treatment of cocaine or METH induced significant reduction in the striatal dopamine and CoQ₁₀ in mice. Cocaine or METH-treated mice exhibited increased thiobarbituric acid reactive substances (TBARs) in the striatum and cerebral cortex without any significant change in the cerebellum. Complex I immunoreactivity was inhibited in both cocaine and METH-treated mice, whereas tyrosine hydroxylase (TH) immunoreactivity was decreased in METH-treated mice and increased in cocaine-treated mice. Neither cocaine nor METH could induce significant change in α-synuclein expression at the doses and duration we have used in the present study. CoQ₁₀ treatment attenuated cocaine and METH-induced inhibition in the striatal ¹⁸F-DOPA uptake as determined by high-resolution microPET neuroimaging. Hence exogenous administration of CoQ₁₀ may provide neuroprotection in drug addiction.     

The effect of interspecific mating on sex ratios in the twospotted spider mite and the Banks grass mite (Acarina: Tetranychidae)

Mixed populations of the twospotted spider mite (TSM),Tetranychus urticae (Koch), and the Banks grass mite (BGM),Oligonychus pratensis (Banks), occur on corn and sorghum plants in late summer in the Great Plains. Interspecific matings between these arrhenotokous species occur readily in the laboratory but yield no female offspring. The effect of interspecific mating on female: male sex ratios was measured by examining the F₁ progeny of females that mated with both heterospecific and conspecific males in no-choice situations. TSM females that mated first with BGM males and then with TSM males produced a smaller percentage of female offspring than TSM females that mated only with TSM males (43.1±5.8 and 78.9±2.8% females, respectively). Similarly, BGM females mated with heterospecific males and then with conspecific males produced fewer female offspring than females mated only with BGM males (55.7±5.2 and 77.5±2.5%, respectively). Lower female: male sex ratios were produced also by BGM females that mated with TSM males after first mating with conspecifics (62.4±3.4%). In mixed populations containing males of both species, females also produced lower female: male sex ratios, but these ratios were not as low as expected based on mating propensities and progeny sex ratios observed in no-choice tests. These data suggest that interspecific mating may substantially reduce female fitness in both mite species by reducing the output of female offspring, but in mixed populations this effect is mitigated by unidentified behavioral mechanisms.