Prolonged milk provisioning in a jumping spider

Science ◽  
2018 ◽  
Vol 362 (6418) ◽  
pp. 1052-1055 ◽  
Author(s):  
Zhanqi Chen ◽  
Richard T. Corlett ◽  
Xiaoguo Jiao ◽  
Sheng-Jie Liu ◽  
Tristan Charles-Dominique ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Parental Care ◽  
Maternal Care ◽  
Offspring Survival ◽  
Animal Kingdom ◽  
Jumping Spider ◽  
Early Stages ◽  
Adult Sex Ratio ◽  
Sexually Mature

Lactation is a mammalian attribute, and the few known nonmammal examples have distinctly different modalities. We document here milk provisioning in a jumping spider, which compares functionally and behaviorally to lactation in mammals. The spiderlings ingest nutritious milk droplets secreted from the mother’s epigastric furrow until the subadult stage. Milk is indispensable for offspring survival in the early stages and complements their foraging in later stages. Maternal care, as for some long-lived vertebrates, continues after the offspring reach maturity. Furthermore, a female-biased adult sex ratio is acquired only when the mother is present. These findings demonstrate that mammal-like milk provisioning and parental care for sexually mature offspring have also evolved in invertebrates, encouraging a reevaluation of their occurrence across the animal kingdom, especially in invertebrates.

The effects of adult sex ratio and density on parental care in Lethrus apterus (Coleoptera, Geotrupidae)

2017 ◽  
Vol 132 ◽  
pp. 181-188 ◽  
Author(s):  
Márta E. Rosa ◽  
Zoltán Barta ◽  
Attila Fülöp ◽  
Tamás Székely ◽  
András Kosztolányi
Keyword(s):  
Sex Ratio ◽  
Parental Care ◽  
Adult Sex Ratio

scholarly journals Flexible parental care: Uniparental incubation in biparentally incubating shorebirds

2017 ◽  
Author(s):  
Martin Bulla ◽  
Hanna Prüter ◽  
Hana Vitnerová ◽  
Wim Tijsen ◽  
Martin Sládeček ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Parental Care ◽  
Evolutionary History ◽  
Single Parent ◽  
Uniparental Care ◽  
Current Population ◽  
Flexible Response ◽  
Adult Sex Ratio ◽  
Incubation Rhythm

Recent findings suggest that relative investment of females and males into parental care depends on the population’s adult sex-ratio. For example, all else being equal, males should be the more caring sex if the sex ratio is male biased. Whether such outcomes are evolutionary fixed (i.e. related to the species’ typical sex-ratio) or whether they arise through flexible responses of individuals to the current population sex-ratio remains unclear. Nevertheless, a flexible response might be limited by evolutionary history when one sex loses the ability to care or when a single parent cannot successfully care. Here, we demonstrate that after the disappearance of one parent, individuals from 8 out of 15 biparentally incubating shorebird species were able to incubate uniparentally for 1-19 days (median = 3,N= 69). Such uniparental phases often resembled the incubation rhythm of species with obligatory uniparental incubation. Although it has been suggested that females of some shorebirds desert their brood after hatching, our findings indicate that either sex may desert prior to hatching. Strikingly, in 27% of uniparentally incubated clutches - from 5 species - we document successful hatching. Our data thus reveal the potential for a flexible switch from biparental to uniparental care.

Reproduction of Richardson's ground squirrel (Spermophilus richardsonii) in southern Saskatchewan

1972 ◽  
Vol 50 (12) ◽  
pp. 1577-1581 ◽  
Author(s):  
D. H. Sheppard
Keyword(s):  
Sex Ratio ◽  
Litter Size ◽  
Ground Squirrel ◽  
Ground Squirrels ◽  
Spermophilus Richardsonii ◽  
Live Trapping ◽  
Native Grassland ◽  
Adult Sex Ratio ◽  
The Mean ◽  
Sexually Mature

Adult Richardson's ground squirrels (n = 238) were collected near Regina, Saskatchewan in April and May of 1969 and 1970. The adult sex ratio (males: females) of collected animals was 1:3.3 compared with a juvenile sex ratio of 1:1 obtained by live trapping in 1967and 1968. The breeding season extended from 3 to 28 April but 77.8% of all conceptions occurred between 7 and 16 April. All yearlings seemed to be sexually mature and the mean litter size for all females baaed on living embryos was 6.93 ± 0.18. Mortality of embryos was 6.83%. Yearlings were smaller than adults but mean litter sizes of yearlings and adults did not differ. Ground squirrels collected from cropland had a significantly larger mean litter size, were somewhat heavier, and had significantly longer humeri than those from native grassland.

scholarly journals Not all sex ratios are equal: the Fisher condition, parental care and sexual selection

2017 ◽  
Vol 372 (1729) ◽  
pp. 20160312 ◽  
Author(s):  
Michael D. Jennions ◽  
Lutz Fromhage
Keyword(s):  
Sex Differences ◽  
Sex Ratio ◽  
Parental Care ◽  
Sex Roles ◽  
Sex Role ◽  
Sex Ratios ◽  
Theoretical Models ◽  
Evolution Of Sex ◽  
Offspring Production ◽  
Adult Sex Ratio

The term ‘sex roles’ encapsulates male–female differences in mate searching, competitive traits that increase mating/fertilization opportunities, choosiness about mates and parental care. Theoretical models suggest that biased sex ratios drive the evolution of sex roles. To model sex role evolution, it is essential to note that in most sexually reproducing species (haplodiploid insects are an exception), each offspring has one father and one mother. Consequently, the total number of offspring produced by each sex is identical, so the mean number of offspring produced by individuals of each sex depends on the sex ratio (Fisher condition). Similarly, the total number of heterosexual matings is identical for each sex. On average, neither sex can mate nor breed more often when the sex ratio is even. But equally common in which sex ratio? The Fisher condition only applies to some reproductive measures (e.g. lifetime offspring production or matings) for certain sex ratios (e.g. operational or adult sex ratio; OSR, ASR). Here, we review recent models that clarify whether a biased OSR, ASR or sex ratio at maturation (MSR) have a causal or correlational relationship with the evolution of sex differences in parental care and competitive traits—two key components of sex roles. We suggest that it is more fruitful to understand the combined effect of the MSR and mortality rates while caring and competing than that of the ASR itself. In short, we argue that the ASR does not have a causal role in the evolution of parental care. We point out, however, that the ASR can be a cue for adaptive phenotypic plasticity in how each sex invests in parental care. This article is part of the themed issue ‘Adult sex ratios and reproductive decisions: a critical re-examination of sex differences in human and animal societies’.

Effects of phytoseiid predators on the sex ratio of the spider mite Panonychus ulmi

1991 ◽  
Vol 69 (1) ◽  
pp. 208-212 ◽  
Author(s):  
Dan L. Johnson ◽  
Heather C. Proctor
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Spider Mite ◽  
Total Population ◽  
Panonychus Ulmi ◽  
Encounter Rate ◽  
Male Mortality ◽  
Adult Sex Ratio ◽  
Biased Sex Ratio ◽  
Male Activity

The effect of predator presence on the adult sex ratio of a spider mite (Panonychus ulmi) was examined in a field experiment. Phytoseiid predators (chiefly Typhlodromus occidentalis) were removed from 32 trees harboring P. ulmi populations, and allowed to remain at natural levels on 32 other trees. Both total population density and proportion of males in the prey population were significantly higher in predator-free trees. Mechanisms that could explain the increase in the proportion of males are examined. The most probable is that greater male activity results in a higher encounter rate between predator and prey, and that subsequent higher male mortality when predators are present exaggerates the female-biased sex ratio. The theoretical effects of sex-biased predation on diplo-diploid and haplo-diploid organisms are discussed.

Population parameters of ringed seals (Phoca hispida Schreber, 1775) in the Svalbard area

1987 ◽  
Vol 65 (4) ◽  
pp. 1021-1027 ◽  
Author(s):  
Christian Lydersen ◽  
Ian Gjertz
Keyword(s):  
Sex Ratio ◽  
Ringed Seal ◽  
Adult Males ◽  
Population Parameters ◽  
Phoca Hispida ◽  
Age Class ◽  
Ringed Seals ◽  
Males And Females ◽  
The Mean ◽  
Sexually Mature

Samples were taken from 284 ringed seals (Phoca hispida) in the Svalbard area during April–July 1981 and March–April 1982. The age of 283 seals was determined by reading annuli in the cementum of the canine teeth. The mean age of the males was 11.3 years, and of the females, 14.9 years. Females were found to be significantly older than males. The mean length of sexually mature ringed seals was 128.9 cm for both sexes. The mean weight of adult males and females was 53.5 and 61.4 kg, respectively. Females were found to be significantly heavier than males. The sex ratio was 47.8% males and 52.2% females. Studies of microscopic sections of testis and epididymis from ringed seal males showed that 63, 75, and 80% of 5-, 6-, and 7-year-old animals, respectively, were sexually mature. The weights of testis and epididymis, diameters of tubuli, and the size of testis all showed a marked increase in the 5-year age-class. Macroscopic sections of ovaries from ringed seal females showed that 20, 60, and 80% of 3-, 4-, and 5-year-old animals, respectively, were sexually mature. The size of the ovaries showed a marked increase in the 5-year age-class. The ovulation rate of ringed seals from Svalbard was calculated to be 0.91.

scholarly journals Sex ratio effects on reproductive strategies in humans

2015 ◽  
Vol 2 (1) ◽  
pp. 140402 ◽  
Author(s):  
Ryan Schacht ◽  
Monique Borgerhoff Mulder
Keyword(s):  
Sexual Selection ◽  
Sex Ratio ◽  
Ethnic Group ◽  
Reproductive Strategies ◽  
Situational Factors ◽  
Male Mating ◽  
Mating Effort ◽  
Short Term ◽  
Adult Sex Ratio ◽  
Using Data

Characterizations of coy females and ardent males are rooted in models of sexual selection that are increasingly outdated. Evolutionary feedbacks can strongly influence the sex roles and subsequent patterns of sex differentiated investment in mating effort, with a key component being the adult sex ratio (ASR). Using data from eight Makushi communities of southern Guyana, characterized by varying ASRs contingent on migration, we show that even within a single ethnic group, male mating effort varies in predictable ways with the ASR. At male-biased sex ratios, men's and women's investment in mating effort are indistinguishable; only when men are in the minority are they more inclined towards short-term, low investment relationships than women. Our results support the behavioural ecological tenet that reproductive strategies are predictable and contingent on varying situational factors.

scholarly journals Is biasing offspring sex ratio adaptive? A test of Fisher's principle across multiple generations of a wild mammal in a fluctuating environment

2018 ◽  
Vol 285 (1891) ◽  
pp. 20181251 ◽  
Author(s):  
Andrea E. Wishart ◽  
Cory T. Williams ◽  
Andrew G. McAdam ◽  
Stan Boutin ◽  
Ben Dantzer ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Tamiasciurus Hudsonicus ◽  
Red Squirrels ◽  
Offspring Sex Ratio ◽  
Offspring Sex ◽  
Adult Sex Ratio ◽  
Secondary Sex Ratio ◽  
North American Red Squirrels ◽  
Negative Frequency Dependent Selection ◽  
Fisher’S Principle

Fisher's principle explains that population sex ratio in sexually reproducing organisms is maintained at 1 : 1 owing to negative frequency-dependent selection, such that individuals of the rare sex realize greater reproductive opportunity than individuals of the more common sex until equilibrium is reached. If biasing offspring sex ratio towards the rare sex is adaptive, individuals that do so should have more grandoffspring. In a wild population of North American red squirrels ( Tamiasciurus hudsonicus ) that experiences fluctuations in resource abundance and population density, we show that overall across 26 years, the secondary sex ratio was 1 : 1; however, stretches of years during which adult sex ratio was biased did not yield offspring sex ratios biased towards the rare sex. Females that had litters biased towards the rare sex did not have more grandoffspring. Critically, the adult sex ratio was not temporally autocorrelated across years, thus the population sex ratio experienced by parents was independent of the population sex ratio experienced by their offspring at their primiparity. Expected fitness benefits of biasing offspring sex ratio may be masked or negated by fluctuating environments across years, which limit the predictive value of the current sex ratio.

Effect of Adult Sex Ratio on Mule Deer and Elk Productivity in Colorado

2001 ◽  
Vol 65 (3) ◽  
pp. 543 ◽  
Author(s):  
Gary C. White ◽  
David J. Freddy ◽  
R. Bruce Gill ◽  
John H. Ellenberger
Keyword(s):  
Sex Ratio ◽  
Mule Deer ◽  
Adult Sex Ratio

scholarly journals Recruitment sex ratios in gray-tailed voles (Microtus canicaudus) in response to density, sex ratio, and season

2003 ◽  
Vol 81 (8) ◽  
pp. 1306-1311 ◽  
Author(s):  
Monica L Bond ◽  
Jerry O Wolff ◽  
Sven Krackow
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Resource Competition ◽  
Sex Ratios ◽  
Female Offspring ◽  
High Population ◽  
Reproductive Value ◽  
High Population Density ◽  
Adult Sex Ratio ◽  
Sex Ratio Adjustment

We tested predictions associated with three widely used hypotheses for facultative sex-ratio adjustment of vertebrates using eight enclosed populations of gray-tailed voles, Microtus canicaudus. These were (i) the population sex ratio hypothesis, which predicts that recruitment sex ratios should oppose adult sex-ratio skews, (ii) the local resource competition hypothesis, which predicts female-biased recruitment at low adult population density and male-biased recruitment at high population density, and (iii) the first cohort advantage hypothesis, which predicts that recruitment sex ratios should be female biased in the spring and male biased in the autumn. We monitored naturally increasing population densities with approximately equal adult sex ratios through the spring and summer and manipulated adult sex ratios in the autumn and measured subsequent sex ratios of recruits. We did not observe any significant sex-ratio adjustment in response to adult sex ratio or high population density; we did detect an influence of time within the breeding season, with more female offspring observed in the spring and more male offspring observed in the autumn. Significant seasonal increases in recruitment sex ratios indicate the capacity of female gray-tailed voles to manipulate their offspring sex ratios and suggest seasonal variation in the relative reproductive value of male and female offspring to be a regular phenomenon.

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