Dolomedes Triton Research Articles

Dolomedes triton

This datasheet on Dolomedes triton covers Identity.

Semi-aquatic spider silks: transcripts, proteins, and silk fibres of the fishing spider, Dolomedes triton (Pisauridae).

To survive in terrestrial and aquatic environments, spiders often rely heavily on their silk. The vast majority of silks that have been studied are from orb-web or cob-web weaving species, leaving the silks of water-associated spiders largely undescribed. We characterize transcripts, proteins, and silk fibres from the semi-aquatic spider Dolomedes triton. From silk gland RNAseq libraries, we report 18 silk transcripts representing four categories of known silk protein types: aciniform, ampullate, pyriform, and tubuliform. Proteomic and structural analyses (scanning electron microscopy, energy dispersive X-ray spectrometry, contact angle) of the D.triton submersible egg sac reveal similarities to silks from aquatic caddisfly larvae. We identified two layers in D.triton egg sacs, notably a highly hydrophobic outer layer with a different elemental composition compared to egg sacs of terrestrial spiders. These features may provide D.triton egg sacs with their water repellent properties.

Abiotic conditions rather than resource availability cues determine aerial dispersal behaviour in spiderlings of Dolomedes triton (Araneae: Pisauridae)

AbstractMany species respond to risks and benefits of dispersal that vary over the short term through condition-dependent dispersal. We used wind tunnels to investigate how abiotic factors, spiderling age, and indicators of environmental quality affect aerial dispersal behaviour of spiderlings in Dolomedes triton (Walckenaer) (Araneae: Pisauridae), a denizen of temporary habitats. More than half of all spiderlings exhibited preballooning, ballooning, or spanning behaviours. Warm temperatures (>22.5 °C) and low wind speeds (<2.0 m/second) increased aerial dispersal. Aerial dispersal behaviour increased significantly until 5 days after hatch, after which it decreased, coinciding with the onset of active hunting by spiderlings. In contrast, cues about ambient food availability (egg sac number and food limitation of the mother) and potential resource competition or risk of cannibalism (conspecific density) did not affect aerial dispersal propensity. Offspring from different females ballooned in different proportions, except at the peak of dispersal, but a female's reproductive output and propensity of her offspring to balloon were uncorrelated. Thus, it appears that spiderlings of D. triton adopt a fixed strategy of high dispersal rate under optimal abiotic conditions, rather than reducing dispersal in response to cues about local food availability or conspecific density.

Energy Efficient Sensor Configuration by Fishing Spider Inspired Mechanism

Wireless sensor networks have inherent characteristics that differ from other wireless networks. Therefore, topology configuration and routing methods in WSNs must address these characteristics. In this paper, we propose an energy efficient clustering model. This model was inspired by the behaviors and capabilities of the six-spotted fishing spider, Dolomedes triton. The suggested model performs cluster-heads selection and clustering in self-organized ways. In order to determine the cluster-heads and the cluster-members, each sensor node uses the local information and simple rules that have been inspired by the Dolomedes triton. We compared our model with a well-known cluster-based routing protocol that uses random fairness for the selection of sensor node cluster-heads. In our computational experiments, we have showed that the energy efficiency and lifetimes of our bio-inspired model exceeds those of the comparison protocol by only using simple bio-inspired mechanism. We also demonstrate our model’s good performance in terms of scalability, which is one of the important indicators of performance for self-organized wireless sensor networks.

Fear, food, sex and parental care: a syndrome of boldness in the fishing spider, Dolomedes triton

We studied individual variation in the antipredator response of the fishing spider, D. triton, in a variety of developmental and behavioural contexts. We examined our data with respect to two general hypotheses: (1) startled spiders should modulate their boldness according to context-specific variables (e.g. developmental stage, feeding opportunities, mating opportunities, parental investment, body condition, etc.), and/or (2) an individual spider's boldness will be consistent (i.e. positively correlated) across contexts such that boldness in any given context is well predicted by boldness in other contexts. We found some support for the former, context-specific hypothesis and strong support for the latter, ‘behavioural-syndromes’ hypothesis. While spiders were significantly bolder in the presence versus absence of prey, boldness did not fluctuate with developmental stage, mating opportunities, parental investment or condition in the manner predicted. Instead, boldness in adult spiders was well predicted by a syndrome of positively correlated bold behaviours across functional contexts. We suggest that animal behaviour most often reflects a combination of context-specific behavioural optimization and context-general expression of behavioural syndromes, as was seen in this experiment. We further suggest that disentangling the relative magnitude of these two general mechanisms in a wide variety of taxa, covering many behavioural-ecological contexts, will provide great insights into (1) population ecology (e.g. the success of invasive/pest species and the failure of threatened species), (2) community ecology (e.g. species coexistence, trophic dynamics), and (3) evolutionary ecology (e.g. evolution of the multivariate behavioural phenotype).

Precopulatory sexual cannibalism in fishing spiders (Dolomedes triton): a role for behavioral syndromes

Precopulatory sexual cannibalism (predation of a potential mate prior to copulation) offers an extreme example of intersexual conflict, a current focus in behavioral ecology. The ‘aggressive-spillover’ hypothesis, posits that precopulatory sexual cannibalism may be a nonadaptive by-product of a general syndrome of voracity (aggression towards prey) that is expressed in multiple behavioral contexts. In this view, selection favoring high levels of voracity throughout ontogeny spills over to cause sexual cannibalism in adult females even when it is not necessarily beneficial. Using the North American fishing spider, Dolomedes triton, we present the first in depth test of this hypothesis. We found support for three aspects of the spillover hypothesis. First, voracity towards hetero-specific prey results in high feeding rates, large adult size, and increased fecundity. Second, juvenile and adult voracity are positively correlated (i.e., voracity is a consistent trait over ontogeny). Third, voracity towards hetero-specific prey is indeed positively correlated with precopulatory sexual cannibalism. Assays of antipredator behavior further revealed positive correlations between boldness towards predators, voracity and precopulatory sexual cannibalism. Overall, our results support the notion that precopulatory sexual cannibalism in D. triton is part of a behavioral syndrome spanning at least three major contexts: foraging, predator avoidance, and mating.

The Role of Body Size in Mating Interactions of the Sexually Cannibalistic Fishing SpiderDolomedes triton

AbstractSome arachnids display extreme sexual size dimorphism (SSD) with adult females being several times larger than adult males. One explanation for SSD in species that exhibit pre‐copulatory sexual cannibalism (female attack, kill and consumption of the male prior to mating) is that smaller males may be less likely victims of predatory attacks by females. However, in some sexually cannibalistic species SSD is relatively moderate (i.e. males are similar in size to females) suggesting benefits of large male body size. Here, I report the results of an experiment designed to explore the ramifications of body size in mating interactions of the sexually cannibalistic, North American fishing spider (Dolomedes triton). Results suggest that male size does not influence courtship behavior, the likelihood of being attacked, or the male's ability to secure a mounting. However, large males were superior at gaining copulations once mounted. Sexual cannibalism may also be predicated on female size. Female condition (mass/cephalothorax area) did not explain any of these behaviors from the copulatory sequence, however, females with a smaller cephalothorax area were more likely to attack courting males. Finally, analysis of the ratio of female size to male size showed that when SSD is weak males are more likely to escape attacks and mate successfully. Results are discussed in light of several hypotheses for sexual cannibalism, and the benefits of large male body size illustrated here are put forth as potential explanations for the relatively moderate extent of SSD found in this sexually cannibalistic species.

WATER SURFACE LOCOMOTION BY SPIDERS: DISTINCT GAITS IN DIVERSE FAMILIES

Abstract Pisaurids such as Dolomedes triton (Walckenaer 1837) are well known as inhabitants of ponds and streams and are adept at locomotion on the water surface. In a broad survey of water surface locomotion in spiders, we have found that most taxa do not use specialized gaits under these circumstances. However, some tetragnathids, araneids, and salticids (three families that are outside of the superfamily Lycosoidea to which the pisaurids belong) resemble D. triton to the extent that they do use specialized gaits when on the water surface. Of these, the tetragnathids are particularly accomplished at water surface locomotion, achieving velocities that exceed those of D. triton when it rows, but not when it gallops.

Trichobothrial mediation of an aquatic escape response: Directional jumps by the fishing spider, Dolomedes triton, foil frog attacks

Fishing spiders (Pisauridae) frequent the surfaces of ponds and streams and thereby expose themselves to predation by a variety of aquatic and semi-aquatic vertebrates. To assess the possibility that the impressive jumps of fishing spiders from the water surface function in evading attacks by frogs, attacks by bullfrogs (Rana catesbiana) and green frogs (R. clamitans) on Dolomedes triton were studied. Both the attack dynamics of the frogs and the evasive behaviors of the spiders were recorded at 250 frames per second. A freeze-dried bullfrog, propelled toward spiders with acceleration, posture, and position that approximated the natural attack posture and dynamics, was used to assess the spiders' behavior. Qualitatively, the spiders responded to these mock-attacks just as they had to attacks by live frogs: jumping (N=29 jumps, 56.9% of instances), rearing the legs nearest the attacking frog (N=15, 29.4%), or showing no visible response (N=7, 13.7%). Spiders that jumped always did so away (in the vertical plane) from the attack (mean =137° vs. vertical at 90° or horizontally toward the frog at 0°). The involvement of the trichobothria (leg hairs sensitive to air movements), and the eyes as sensory mediators of the evasion response was assessed. Spiders with deactivated trichobothria were significantly impaired relative to intact and sham-deactivated spiders, and relative to spiders in total darkness. Thus, functional trichobothria, unlike the eyes, are both necessary and sufficient mediators of the evasion response. Measurements of air flow during frog attacks suggest that an exponential rise in flow velocity is the airborne signature of an attack.

HABITAT AFFINITIES OF SPIDERS LIVING NEAR A FRESHWATER POND

Habitat ranges of ground-dwelling spiders were studied by pitfall trapping in and around a freshwater pond during the spring and summer of 1998 in central Alberta, Canada. Sixty species from 14 families were collected, and catches of several species suggested distinct habitat affinities along transects between the pond and adjacent terrestrial habitats. Variation in the catches of Pirata piraticus (Clerck 1757), Pardosa moesta Banks 1892, Pardosa fuscula (Thorell 1875), and immature Pirata species were partially explained by soil moisture at trap locations extending from the shore. We devised a “floating” pitfall trap that captured several species, including mature and immature Dolomedes triton (Walckenaer 1837), Pirata piraticus, and other immature Lycosidae, directly on the water surface. A DCA ordination revealed distinct spider assemblages were associated with three habitat types: 1) the water surface; 2) the moist habitats closely associated with the water's edge; and 3) the drier, terrestrial grassland habitats located >2 m from the shore. A new, more inclusive definition of semi-aquatic spiders was developed, based on knowledge about both male and female activity near the shore, and affinities towards soil moisture. Thus, Pirata piraticus, Dolomedes triton, and Pardosa fuscula were defined as semi-aquatic spiders.

Trichobothrial mediation of an aquatic escape response: Directional jumps by the fishing spider, Dolomedes triton, foil frog attacks

Fishing spiders (Pisauridae) frequent the surfaces of ponds and streams and thereby expose themselves to predation by a variety of aquatic and semi-aquatic vertebrates. To assess the possibility that the impressive jumps of fishing spiders from the water surface function in evading attacks by frogs, attacks by bullfrogs (Rana catesbiana) and green frogs (R. clamitans) on Dolomedes triton were studied. Both the attack dynamics of the frogs and the evasive behaviors of the spiders were recorded at 250 frames per second. A freeze-dried bullfrog, propelled toward spiders with acceleration, posture, and position that approximated the natural attack posture and dynamics, was used to assess the spiders' behavior. Qualitatively, the spiders responded to these mock-attacks just as they had to attacks by live frogs: jumping (N=29 jumps, 56.9% of instances), rearing the legs nearest the attacking frog (N=15, 29.4%), or showing no visible response (N=7, 13.7%). Spiders that jumped always did so away (in the vertical plane) from the attack (mean =137 degrees vs. vertical at 90 degrees or horizontally toward the frog at 0 degrees ). The involvement of the trichobothria (leg hairs sensitive to air movements), and the eyes as sensory mediators of the evasion response was assessed. Spiders with deactivated trichobothria were significantly impaired relative to intact and sham-deactivated spiders, and relative to spiders in total darkness. Thus, functional trichobothria, unlike the eyes, are both necessary and sufficient mediators of the evasion response. Measurements of air flow during frog attacks suggest that an exponential rise in flow velocity is the airborne signature of an attack.

Trichobothrial mediation of an aquatic escape response: Directional jumps by the fishing spider, Dolomedes triton, foil frog attacks

Fishing spiders (Pisauridae) frequent the surfaces of ponds and streams and thereby expose themselves to predation by a variety of aquatic and semi-aquatic vertebrates. To assess the possibility that the impressive jumps of fishing spiders from the water surface function in evading attacks by frogs, attacks by bullfrogs (Rana catesbiana) and green frogs (R. clamitans) on Dolomedes triton were studied. Both the attack dynamics of the frogs and the evasive behaviors of the spiders were recorded at 250 frames per second. A freeze-dried bullfrog, propelled toward spiders with acceleration, posture, and position that approximated the natural attack posture and dynamics, was used to assess the spiders' behavior. Qualitatively, the spiders responded to these mock-attacks just as they had to attacks by live frogs: jumping (N=29 jumps, 56.9% of instances), rearing the legs nearest the attacking frog (N=15, 29.4%), or showing no visible response (N=7, 13.7%). Spiders that jumped always did so away (in the vertical plane) from the attack (mean =137° vs. vertical at 90° or horizontally toward the frog at 0°). The involvement of the trichobothria (leg hairs sensitive to air movements), and the eyes as sensory mediators of the evasion response was assessed. Spiders with deactivated trichobothria were significantly impaired relative to intact and sham-deactivated spiders, and relative to spiders in total darkness. Thus, functional trichobothria, unlike the eyes, are both necessary and sufficient mediators of the evasion response. Measurements of air flow during frog attacks suggest that an exponential rise in flow velocity is the airborne signature of an attack.

Sexual cannibalism in fishing spiders (Dolomedes triton): an evaluation of two explanations for female aggression towards potential mates

I manipulated food availability in juvenile and adult fishing spiders (Dolomedes triton) to test two hypotheses for sexual cannibalism. The adaptive foraging hypothesis posits that sexual cannibalism is an economic, adaptive foraging strategy on the part of the adult female. In contrast, the aggressive-spillover hypothesis suggests that precopulatory sexual cannibalism is misplaced aggression favoured in previous life-history phases. Several results indicated support for the adaptive foraging hypothesis. First, increased adult food availability produced marginally nonsignificant fecundity benefits in female's first egg sacs and highly significant fecundity benefits in female's second egg sacs. Second, while consumption of a male did not result in more offspring in either egg sac, it did significantly increase the probability a female would successfully hatch an egg sac. Finally, mating trials revealed mixed support for the adaptive foraging hypothesis as, for the most part, female mating behaviour (attack or mate) was not determined by the adaptive value a male represented (food item or sperm donor). Specifically, the likelihood of a precopulatory attack was not determined by male size, date (an indirect estimate of male availability) or female nutrient load. However, mated females did tend to attack courting males more often than virgin females. The aggressive-spillover hypothesis was supported by several findings. For juveniles, food availability had a significant positive effect on fixed female size (cephalothorax area at final moult) which, in turn, had a significant positive effect on fecundity. Thus, the spillover hypothesis' assertion that strong fecundity selection acts on juvenile feeding and fixed adult size was supported. The possibility that the spillover and adaptive foraging hypotheses are not mutually exclusive is discussed, especially in light of the presence of high levels of sexual cannibalism both before and after mating.

Prey availability limits fecundity and influences the movement pattern of female fishing spiders.

We conducted a food supplementation field experiment to test two hypotheses: (1) fecundity of the fishing spider Dolomedes triton is limited by a shortage of prey, and (2) the increased movement of adult female D. triton exhibited upon maturation is a foraging adaptation to lessen the impact of food limitation on egg production. Free ranging, uniquely marked adult female fishing spiders were assigned either to a food-supplemented group that received crickets in addition to their natural diet, or to a control group. Juvenile female spiders were also marked and their movement patterns were recorded, but juveniles were not offered supplemental food. Food-supplemented adult females gained weight at a faster rate and hatched more than twice as many offspring as control females. Adult females in the control group moved greater distances per day than did juvenile females. Supplemented adult females moved shorter distances per day than control females, and the movement pattern of fed adults did not differ from that of juveniles. These results support the hypotheses that adult female D. triton are food limited, and that the increased movement of adult females is a switch in foraging behavior that occurs during the reproductive period. Our finding that natural prey shortages limit egg production contrasts with laboratory-based studies of food limitation in the genus Dolomedes, and contradicts a basic assumption of a recent hypothesis that sexual cannibalism in Dolomedes is non-adaptive. These discrepancies highlight the importance of insights gained from field experiments with natural populations.

SPIDER SIZE AND LOCOMOTION ON THE WATER SURFACE (ARANEAE, PISAURIDAE)

Abstract Newly emerged fishing spiders, Dolomedes triton (Walckenaer 1837), can achieve rowing velocities as high as those of adults despite an approximately 600-fold difference in mass (1.7 mg vs. 1.1 g). In contrast, when velocity is measured in relative terms (body lengths/sec), small spiders move much more rapidly than adults, with Vrel ∝ mass−0.31. This surprising performance of very small spiders can be attributed both to their very high stride frequency (fs ∝ mass−0.43) and to the high angular velocity of their propulsive legs (ω ∝ mass−0.33). Calculations of leg tip velocities, based on measurements of both angular velocities and leg lengths, reveal that maximum leg tip velocities are achieved by spiders of about 33 mg, nineteen times more massive than the smallest spiders we tested. Some very small spiders perform conspicuously and consistently less well than do others of the same size. A detailed dissection of the motion of these underachievers reveals that a disproportionate amount of their row...

Locomotion on the water surface: hydrodynamic constraints on rowing velocity require a gait change

Fishing spiders, Dolomedes triton (Araneae, Pisauridae), propel themselves across the water surface using two gaits: they row with four legs at sustained velocities below 0.2 m s(-)(1) and they gallop with six legs at sustained velocities above 0.3 m s(-)(1). Because, during rowing, most of the horizontal thrust is provided by the drag of the leg and its associated dimple as both move across the water surface, the integrity of the dimple is crucial. We used a balance, incorporating a biaxial clinometer as the transducer, to measure the horizontal thrust forces on a leg segment subjected to water moving past it in non-turbulent flow. Changes in the horizontal forces reflected changes in the status of the dimple and showed that a stable dimple could exist only under conditions that combined low flow velocity, shallow leg-segment depth and a long perimeter of the interface between the leg segment and the water. Once the dimple disintegrated, leaving the leg segment submerged, less drag was generated. Therefore, the disintegration of the dimple imposes a limit on the efficacy of rowing with four legs. The limited degrees of freedom in the leg joints (the patellar joints move freely in the vertical plane but allow only limited flexion in other planes) impose a further constraint on rowing by restricting the maximum leg-tip velocity (to approximately 33 % of that attained by the same legs during galloping). This confines leg-tip velocities to a range at which maintenance of the dimple is particularly important. The weight of the spider also imposes constraints on the efficacy of rowing: because the drag encountered by the leg-cum-dimple is proportional to the depth of the dimple and because dimple depth is proportional to the supported weight, only spiders with a mass exceeding 0.48 g can have access to the full range of hydrodynamically possible dimple depths during rowing. Finally, the maximum velocity attainable during rowing is constrained by the substantial drag experienced by the spider during the glide interval between power strokes, drag that is negligible for a galloping spider because, for most of each inter-stroke interval, the spider is airborne. We conclude that both hydrodynamic and anatomical constraints confine rowing spiders to sustained velocities lower than 0.3 m s(-)(1), and that galloping allows spiders to move considerably faster because galloping is free of these constraints.

The Interaction of Temperature, Dissolved Oxygen and Predation Pressure in an Aquatic Predator-Prey System

We examined the effects of the physical environment on the outcome of predatory encounters between tadpoles of the frog Rana clamitans and the fishing spider, Dolomedes triton. These species co-occur in pond habitats that vary widely in dissolved oxygen and temperature. Water temperature and oxygen levels have complex effects on the behavior of anuran larvae. Behavioral responses induced by shifting physiological requirements can increase the risk of predation on tadpoles. We experimentally manipulated treatment levels of both dissolved oxygen and temperature in trials conducted between individual predators (Dolomedes) and single prey (Rana). Environmental conditions had significant effects on the behavior of tadpoles that increased the risk of attack by Dolomedes. Under the low oxygen condition, more tadpoles were eaten, and the total amount of time spent at the surface and the number of times surfaced per minute were significantly greater. For Dolomedes, increased tadpole activity resulted in the increased expression of several predatory behaviors. We found significant treatment and interaction effects on the expression of both resting and ambush postures. In addition, survival analyses showed a significantly earlier expression of predatory behaviors in decreased oxygen level treatments.

Phenology and life-cycle regulation of the fishing spider Dolomedes triton Walckenaer (Araneae, Pisauridae) in central Alberta

Dolomedes triton Walckenaer, a widespread and common fishing spider in North America, has a semivoltine life cycle in central Alberta, Canada. Juvenile spiders hibernate twice. According to evidence from laboratory rearings and patterns in field collections, the main overwintering stages are instars 3-5 and 9-11. After the second overwintering period, large juveniles moult once or twice to reach the reproductive adult stage. Juveniles grow rapidly between May and August but during overwintering between September and April, virtually no growth (measured as maximum carapace width of individuals) was observed in field populations. Dolomedes triton has a variable number of juvenile stages, ranging from 10 to 15 in males and from 9 to 15 in females. Both overwintering phases are facultative even though most individuals overwinter twice in central Alberta: at high temperatures (24-25°C) and under long-day conditions (either 18 h light : 6 h dark or 19 h light : 5 h dark) juveniles can develop directly to adults. Short-day photoperiods did not prolong stage durations, but warm periods, when experienced late in development only, were associated with extra moults, and may thus delay maturation until the following spring. Although the second overwintering period is a quiescence regulated strictly by temperature, regulation of the first overwintering period is more complex, including probable preconditioning through interaction of temperature and photoperiod.

Locomotion on the water surface: propulsive mechanisms of the fisher spider

Using kinematic and mechanical experiments, we have shown how fisher spiders, Dolomedes triton (Araneae, Pisauridae), can generate horizontal propulsive forces using their legs. This horizontal thrust is provided primarily by the drag of the leg and its associated dimple as both move across the water surface. Less important sources of resistance are surface tension and bow waves. The relative contributions of drag, surface tension and bow waves were examined in several different ways. In one experiment, we measured the forces acting on a leg segment as water flowed past it in non-turbulent flow; the bow wave was not present at leg relative velocities below 0.2ms-1 and thus cannot play a role in thrust production at low leg speeds. In a second experiment, we varied the surface tension by altering the concentration of ethanol from 0% to 9% in the experimental water tank. At a constant dimple depth, force varied little with changes in surface tension, a result consistent with the hypothesis that drag is the primary source of resistance. In addition, however, as surface tension decreased from 0.072 to 0.064Nm-1, the power exponent of the relationship between force and velocity (as measured by the exponent of the power function relating the two variables) increased; at lower surface tensions, down to 0.054Nm-1, the power exponent of the relationship between force and velocity decreased. These results suggest an influence of surface tension (albeit still secondary to drag) in generating horizontal resistance to leg movement. We also measured flow disturbance in the water downstream from a leg segment and confirmed that, even at velocities well below 0.2ms-1, the leg-cum-dimple transferred momentum to the water, which is a clear indication that drag is a contributor to the resistance encountered by a spider's leg. Finally, modeling the leg-cum-dimple as a circular cylinder generates values of drag that account for 75­98% of the measured leg force when the dimple is 0 or 1mm deep. These results not only elucidate the primary mechanism of propulsion for D. triton and other similar-sized arthropods, such as adult water striders (Gerridae), but also suggest that the formerly enigmatic locomotion of very small water-walking organisms (e.g. first-instar water striders) can be understood in the same way.

Effects of Food Limitation and Sexual Cannibalism on Reproductive Output of the Nursery Web Spider Dolomedes triton (Araneae: Pisauridae)

Reproductive output of free-ranging females of Dolomedes triton was not constrained by natural food limits in relation to that of sated spiders held in field cages. A two-year study revealed both seasonal and annual variation in egg number and egg-sac development time that was driven by factors other than food availability. There was a strong, positive correlation between egg numbers in first and second egg-sacs; some females produced three egg sacs under field conditions. In an experiment using field cages, reproductive output was affected by food availability to adults, female body size measured as carapace width, and by interaction between these two variables. Under both ambient field conditions and experimentally maintained satiation, fecundity increased linearly with carapace width. However, larger females failed to achieve their full, reproductive potential when food was scarce, although reproductive output of smaller females was unaffected. Females of D. triton allowed to feed on their mates did not show increased reproductive output or rate and thus do not receive any special nutrient supplements through sexual cannibalism.