Opercular Flaps as Sexual Ornaments for Male Longear Sunfish (Lepomis megalotis): Male Condition and Male-Male Competition

Male longear sunfish, Lepomis megalotis , have longer opercular flaps than females, and females are known to prefer males with longer flaps, suggesting that these exaggerated structures serve as sexual ornaments. We tested the hypothesis that opercular flap length is associated with body condition and is therefore potentially an honest indicator of male quality. Opercular flaps grew significantly faster than pelvic fin spines, a non-sexually selected trait, regardless of diet treatment, suggesting an advantage to having fast-growing opercular flaps. Growth indices (opercular flap growth divided by pelvic fin spine growth) of males fed a larger ration were greater than those of males fed a smaller ration, although the difference was marginally non-significant. We also tested for an effect of opercular flap length on resource holding power by manipulating flap length on pairs of males matched for body length. In an experiment where opercular flaps were clipped to different lengths, only longer original (unmanipulated) flap length was associated with a significantly greater frequency of dominance. In a corollary experiment where opercular flaps were artificially lengthened, the abnormally long-flapped males were dominant significantly more often than the 'normal' males given transparent extensions. These results indicate that the opercular flap length of male longear sunfish may serve as an honest indicator of male quality and may be used to assess the resource holding power of rival males.     

Hypoxia-induced developmental plasticity of larval growth,gill and labyrinth organ morphometrics in two anabantoid fish: The facultative air-breather Siamese fighting fish (Betta splendens) and the obligate air-breather the blue gourami (Trichopodus trichopterus)

Larval and juvenile air breathing fish may experience nocturnal and/or seasonal aquatic hypoxia. Yet, whether hypoxia induces respiratory developmental plasticity in larval air breathing fish is uncertain. This study predicted that larvae of two closely related anabantid fish—the facultative air breather the Siamese fighting fish (Betta splendens) and the obligate air breathing blue gourami (Trichopodus trichopterus)—show distinct differences in developmental changes in body, gill, and labyrinth morphology because of their differences in levels of dependency upon air breathing and habitat. Larval populations of both species were reared in normoxia or chronic nocturnal hypoxia from hatching through 35–38 days postfertilization. Gill and labyrinth variables were measured at the onset of air breathing. Betta splendens reared in normoxia possessed larger, more developed gills (~3× greater area) than T. trichopterus at comparable stages. Surface area of the emerging labyrinth, the air breathing organ, was ~ 85% larger in normoxic B. splendens compared to T. trichopterus. Rearing in mild hypoxia stimulated body growth in B. splendens, but neither mild nor severe hypoxia affected growth in T. trichopterus. Condition factor, K (~ 1.3 in B. splendens, 0.7 in T. trichopterus) was unaffected by mild hypoxia in either species, but was reduced by severe hypoxia to <0.9 only in B. splendens. Severe, but not mild, hypoxia decreased branchial surface area in B. splendens by ~40%, but neither hypoxia level affected Trichopodus branchial surface. Mild, but not severe, hypoxia increased labyrinth surface area by 30% in B. splendens. However, as for branchial surface area, labyrinth surface area was not affected in Trichopodus. These differential larval responses to hypoxic rearing suggest that different larval habitats and activity levels are greater factors influencing developmental plasticity than genetic closeness of the two species.     

Mate Choice and Spawning Success in the Fighting Fish Betta splendens: the Importance of Body Size, Display Behavior and Nest Size

Courtship displays should be exaggerated enough to attract mates and yet tempered so as not to deter them. We tested this hypothesis in the fighting fish Betta splendens by studying courtship displays and body size and their relationships with male parental quality and female fecundity, as well as the effects of display behavior and body size on mate choice decisions and spawning success. Because of their high degree of parental investment, males are expected to be discriminating in their choice of mates. Males who displayed more frequently built larger nests, a measure of parental quality, but larger males did not. When females were paired with males with high display rates, however, the pair had fewer eggs in their nest, even when accounting for female body mass. In a mate choice test using computer‐generated male stimuli that differed only in display behavior, females showed no preferences for displaying males vs. non‐displaying males, or for males with higher display rates vs. lower display rates. In similar tests in which the computer‐generated males differed only in size, females preferred larger males, but also preferred males that differed with respect to body size (negative assortative mating). Males preferred computer‐generated females that performed courtship displays over non‐displaying females, but showed no preferences for female body size. Neither a female's body size nor her display behavior was a significant predictor of her fecundity as estimated by the number of eggs released during spawning. Thus, our results suggest that female B. splendens must balance male parental quality (nest size) with the risk of potentially disruptive or dangerous behavior during spawning, and that females may minimize these risks through negative size‐assortative mating. Female display behavior, while unrelated to fecundity in our study, may attract males because it indicates reproductive readiness or serves a species‐recognition function.     

Directional female preference for an exaggerated male trait in canary (Serinus canaria) song

Motor constraints on vocal production impose a trade-off between trill rate and frequency bandwidth within birdsong. We tested whether domesticated canary (Serinus canaria) females, reared either in acoustic isolation or in aviary conditions, had a preference for broad bandwidth songs with artificially increased syllable rates. The copulation solicitation display (CSD) was used as an index of female preference. As predicted, both naive and experienced females were especially responsive to syllables with a broad bandwidth emitted at an artificially increased rate. Female preference for supernormal stimuli provide support for the honest-signalling hypothesis and our results are consistent with recent findings indicating that production of song phrases maximizing both bandwidth and syllable rate may be a reliable indicator of male physical or behavioural qualities. We suggest that female preference for vocal emissions, which simultaneously maximize these two parameters, could be a widespread pattern within songbirds.     

Critical role of hypoxia and A2A adenosine receptors in liver tissue-protecting physiological anti-inflammatory pathway

Whole body exposure of wild type control littermates and A2A adenosine receptor (A2AR) gene deleted mice to low oxygen containing inspired gas mixture allowed the investigation of the mechanism that controls inflammatory liver damage and protects the liver using a mouse model of T cell-mediated viral and autoimmune hepatitis. We tested the hypothesis that the inflammatory tissue damage-associated hypoxia and extracellular adenosine --> A2AR signaling plays an important role in the physiological anti-inflammatory mechanism that limits liver damage during fulminant hepatitis. After induction of T cell-mediated hepatitis, mice were kept in modular chambers either under normoxic (21% oxygen) or hypoxic (10% oxygen) conditions for 8 h. It was shown that the whole body exposure to hypoxic atmosphere caused tissue hypoxia in healthy animals as evidenced by a decrease in the arterial blood oxygen tension and increase of the plasma adenosine concentration (P < 0.05). This "hypoxic" treatment resulted in significantly reduced hepatocellular damage and attenuated levels of serum cytokines in mice with acute liver inflammation. The anti-inflammatory effects of hypoxia were not observed in the absence of A2AR in studies of A2AR gene-deficient mice or when A2AR have been pharmacologically antagonized with synthetic antagonist. The presented data demonstrate that total body hypoxia-triggered pathway provides protection in acute hepatitis and that hypoxia (upstream) and A2AR (downstream) function in the same immunosuppressive and liver tissue-protecting pathway.     

Replication catastrophe induced by cyclic hypoxia leads to increased APOBEC3B activity

Tumor heterogeneity includes variable and fluctuating oxygen concentrations, which result in the accumulation of hypoxic regions in most solid tumors. Tumor hypoxia leads to increased therapy resistance and has been linked to genomic instability. Here, we tested the hypothesis that exposure to levels of hypoxia that cause replication stress could increase APOBEC activity and the accumulation of APOBEC-mediated mutations. APOBEC-dependent mutational signatures have been well-characterized, although the physiological conditions which underpin them have not been described. We demonstrate that fluctuating/cyclic hypoxic conditions which lead to replication catastrophe induce the expression and activity of APOBEC3B. In contrast, stable/chronic hypoxic conditions which induce replication stress in the absence of DNA damage are not sufficient to induce APOBEC3B. Most importantly, the number of APOBEC-mediated mutations in patient tumors correlated with a hypoxia signature. Together, our data support the conclusion that hypoxia-induced replication catastrophe drives genomic instability in tumors, specifically through increasing the activity of APOBEC3B.     

Cardiovagal regulation during combined hypoxic and orthostatic stress: fainters vs. nonfainters.

We tested the hypothesis that individual differences in the effect of acute hypoxia on the cardiovagal arterial baroreflex would determine individual susceptibility to hypoxic syncope. In 16 healthy, nonsmoking, normotensive subjects (8 women, 8 men, age 20-33 yr), we assessed orthostatic tolerance with a 20-min 60 degrees head-upright tilt during both normoxia and hypoxia (breathing 12% O(2)). On a separate occasion, we assessed baroreflex control of heart rate (cardiovagal baroreflex gain) using the modified Oxford technique during both normoxia and hypoxia. When subjects were tilted under hypoxic conditions, 5 of the 16 developed presyncopal signs or symptoms, and the 20-min tilt had to be terminated. These "fainters" had comparable cardiovagal baroreflex gain to "nonfainters" under both normoxic and hypoxic conditions (normoxia, fainters: -1.2 +/- 0.2, nonfainters: -1.0 +/- 0.2 beats.min(-1).mmHg(-1), P = 0.252; hypoxia, fainters: -1.3 +/- 0.2, nonfainters: -1.0 +/- 0.1 beats.min(-1).mmHg(-1), P = 0.208). Furthermore, hypoxia did not alter cardiovagal baroreflex gain in either group (both P > 0.8). It appears from these observations that hypoxic syncope results from the superimposed vasodilator effects of hypoxia on the cardiovascular system and not from a hypoxia-induced maladjustment in baroreflex control of heart rate.     

Skin mild hypoxia enhances killing of UVB-damaged keratinocytes through reactive oxygen species-mediated apoptosis requiring Noxa and Bim

The naturally occurring skin hypoxia has emerged as a crucial host factor of the epidermal microenvironment. We wanted to systematically investigate how reduced oxygen availability of the epidermis modulates the response of keratinocytes and melanocytes to noxious ultraviolet B radiation (UVB). We report that the exposure of normal human keratinocytes (NHKs) or melanocytes (NHEMs) to mild hypoxia drastically impacts cell death responses following UVB irradiation. The hypoxic microenvironment favors survival and reduces apoptosis of UVB-irradiated NHEMs and their malignant counterparts (melanoma cells). In contrast, NHKs, but not the transformed keratinocytes, under hypoxic conditions display increased levels of reactive oxygen species (ROS) and are significantly sensitized to UVB-mediated apoptosis as compared to NHKs treated under normoxic conditions. Prolonged exposure of UVB-treated NHKs to hypoxia triggers a sustained and reactive oxygen species-dependent activation of the stress kinases p38(MAPK) and JNKs, which in turn, engage the activation of Noxa and Bim proapoptotic proteins. Combined silencing of Noxa and Bim significantly inhibits UVB-mediated apoptosis under hypoxic conditions, demonstrating that hypoxia results in an amplification of the intrinsic apoptotic pathway. Physiologically occurring skin hypoxia, by facilitating the specific removal of UVB-damaged keratinocytes, may represent a decisive host factor impeding important steps of the photocarcinogenesis process.     

Seasonal Differences in Hypoxia Tolerance in Gulf Killifish, Fundulus Grandis (Fundulidae)

Many estuarine habitats are characterized by episodes of hypoxia, the frequency and severity of which may vary seasonally. Accordingly, resident fish species may show seasonal differences in their capacity to tolerate hypoxia. We have tested this hypothesis in the gulf killifish, Fundulus grandis, sampled from the Lake Pontchartrain estuary (Louisiana) at different times of the year. We measured 2 indicators of hypoxia tolerance, the frequency of aquatic surface respiration (ASR) during gradual reduction in dissolved oxygen (D.O.) and survival time during severe hypoxic stress, and found both to be significantly affected by season. Fish collected during the summer did not engage in ASR until the D.O. concentration dropped to values lower than that required to elicit ASR by fish collected during other seasons. Laboratory acclimation of fish to low oxygen did not change the relationship between ASR behavior and D.O., suggesting that the observed seasonal effect on ASR was not simply due to previous exposure of summer fish to environmental hypoxia. Furthermore, fish collected during the summer and winter had significantly longer survival times during exposure to severe hypoxia than fish collected during the fall. Survival analysis indicated that the condition of fish was positively associated with survival time, and seasonal variation in condition accounted for about half of the observed difference between survival times of fish collected during the summer and fall. Seasonal variation in ASR and survival, when taken together, demonstrate that hypoxia tolerance in F. grandis may be subject to acclimatization. An increase in hypoxia tolerance during the summer could increase survivorship of fish when exposed to elevated temperatures and low oxygen concentrations which prevail during the summer months.     

Male mate choice in a sexually cannibalistic species: male escapes from hungry females in the praying mantid <Emphasis Type="Italic">Tenodera angustipennis</Emphasis>

While competing males and choosy females may be common in animal mating systems, male choice can evolve under certain conditions. Sexual cannibalism is such a condition because of the high mortality risk for males. In mantids, female body condition is associated with male mate preference, with fat females preferred, due to at least two reasons: females in poor nutritional condition are likely to attack and predate males, and fat females can potentially increase the number of offspring. Thus, the risk of cannibalism and female fecundity can influence male mating behavior. In this study, we attempted to separate these factors by using the praying mantid Tenodera angustipennis to examine whether male preference for fat female mantids was based on avoiding sexual cannibalism (cannibalism avoidance hypothesis) or preference for female fecundity (fecundity preference hypothesis). The feeding regimes were experimentally manipulated to discriminate between the effects of female fecundity and female hunger status on male and female mating behaviors. We found that recently starved females more frequently locomoted toward the male, and that male abdominal bending was less intensive and escape was sooner from recently starved females. These female and male behavioral responses to female hunger condition may reveal male avoidance of dangerous females in this mantid.     

Inhibitory effects of hyperthermia on mechanisms involved in autoresuscitation from hypoxic apnea in mice: a model for thermal stress causing SIDS.

The physiological mechanisms that might be involved in an association between heat stress and sudden infant death syndrome (SIDS) are obscure. We tested the hypothesis that a combination of acute hypoxia and elevated body temperature (T(B)) might prevent autoresuscitation from hypoxic apnea (AR). We exposed 21-day-old mice (total = 216) to hyperthermia (40.5-43.5 degrees C), hypoxia, or a combination of the two. Neither hyperthermia alone (40.5-42.5 degrees C) nor hypoxia alone was found to be lethal, but the combination produced failure to AR during the first hypoxic exposure with increasing frequency as T(B) increased. The ability to withstand multiple hypoxic exposures was also reduced as T(B) increased. In contrast, heat stress causing moderate T(B) increase (40.5 degrees C) had no effect on survival. Increased T(B) (43.5 degrees C) reduced gasping duration and number of gasps. It increased heart rate during anoxia but did not alter gasping rate. Furthermore, the oxygen-independent increase in heart rate observed before gasping failure was usually delayed until after the last gasp in hyperthermic animals. Mild dehydration occurred during T(B) elevation, but this did not appear to be a primary factor in AR failure. We conclude that a thermal stress, which by itself is nonlethal, frequently prevents AR from hypoxic apnea. This may be due, at least in part, to decreased gasp number and duration as well as to hyperthermia-related asynchrony of reflexes regulating heart and gasping frequencies during attempted AR.     

Instrumental conditioning of choice behavior in male Siamese fighting fish (Betta splendens)

Despite the differences in the response of male Betta splendens toward various stimuli, no research has attempted to determine the preference for a live conspecific versus a mirror presentation. A submerged T-maze was used to present both stimuli to healthy male B. splendens (N=16). The results indicated that subjects' start box and swimway latencies decreased significantly over the 30 trials. Moreover, the analysis of choices demonstrated a modest, but statistically significant, preference for the live conspecific over the mirror presentation. The results are discussed in terms of the stimuli qualities that elicit an aggressive response in B. splendens and the implications for common experimental procedures.     

Do Displays Send Information about Ornament Structure and Male Quality in the Ornate Tree Lizard,Urosaurus ornatus?

Displays can transmit information about ornament or male quality; however, few studies have simultaneously explored the relationship between displays, ornament and male quality within a single species. We quantified ornament morphology (five throat color morphs, throat area, and belly area), male quality (bite force, sprint speed, body condition, and body mass), display behavior [percent time displaying (PTD), number of pushups per display, and display duration], and movement behavior among males in a population of the ornate tree lizard, Urosaurus ornatus. Previous studies have shown that male U. ornatus are polymorphic in throat coloration and that morphs differ in behavioral aggression. Our study shows that blue throat morphs use 1.5 more pushups per display than other male color morphs, which suggests that throat color and display behavior act as backup signals for aggression. However, other data support the multiple messages hypothesis, and overall our data do not provide conclusive evidence for any one hypothesis. In addition, we show that body mass is positively related to both PTD and percent time moving and this relationship is independent of color morph. We also found that throat area, belly area, bite force, sprint speed, and body condition are unrelated to display behavior. This result highlights at least some discordance between display behavior, ornaments, and performance in U. ornatus and suggests that these traits may be evolving independently.     

Chronic CO exposure stimulates erythropoiesis but not glomus cell growth

The effect of chronic CO exposure, which stimulates erythropoietin production and erythropoiesis, was studied on carotid body cells in the rat. The hypothesis to be tested was that chronic CO inhalation would stimulate cellular hypertrophy and hyperplasia of carotid body if it caused local tissue hypoxia as in chronic hypoxia. The failure of an appropriate response would indicate a lack of a specific local effect on carotid body tissue PO2 presumably because of its unusually high tissue blood flow. Six young male rats were exposed to 0.4-0.5 Torr (0.05-0.07%) inspired PCO in air for 22 days. Control rats (n = 6) were maintained under similar conditions except for CO exposure. After the exposure period the rats were anesthetized, blood was collected for hematocrit, and the carotid bodies were surgically exposed and fixed for electron microscopy and morphometry of type I and type II cells and capillary endothelium. Hematocrit was significantly greater in the CO-exposed group (75 vs. 48%), whereas no significant difference was found in the carotid body parenchyma between the control and CO-exposed groups. We conclude that the lack of an effect of chronic CO exposure on the carotid bodies in contrast to the strong erythropoietic response indicates a relatively high tissue blood flow rate in the carotid body and that CO did not exert a direct cellular effect. The results also suggest that the hypertrophic response of carotid body glomus cells to chronic hypoxic hypoxia is the result of a local direct effect of low PO2 rather than secondary to systemic effects.     

Aerial and aquatic respiration of the Australian desert goby, Chlamydogobius eremius

Physiological, anatomical and behavioural adaptations enable the Australian desert goby, Chlamydogobius eremius, to live in mound springs and temporary aquatic habitats surrounding the south-eastern rim of the Lake Eyre drainage basin in the harsh inland of Australia. This study describes the desert goby's respiratory and metabolic responses to hypoxic conditions and its use of buccal air bubbles for gas exchange at the water surface. Oxygen consumption for C. eremius is significantly higher in water than in air under normoxic and hypoxic conditions. In water, total oxygen consumption (V(O(2))) increases from normoxic conditions (253 microl g(-1) h(-1)) to 8% ambient O(2) concentration (377 microl g(-1) h(-1)), then decreases with increasing hypoxia of 4% O(2) (226 microl g(-1) h(-1)) and at 2% O(2) (123 microl g(-1) h(-1)). In air (fish were moist but out of water), V(O(2)) progressively decreases from normoxic conditions to hypoxic conditions (21% O(2), V(O(2)) is 169 microl g(-1) h(-1) to 39 microl g(-1) h(-1) at 2% O(2)). These data indicate oxygen-conforming patterns with increasing hypoxia both in air and in water below 8% O(2). In water, opercular movement rates remain unchanged with increasing hypoxia (139 min(-1) at 21% O(2), 154 min(-1) at 8%, 156 min(-1) at 4% and 167 min(-1) at 2%) but in air, opercular movement rates are significantly lower than in water, corresponding with the lower metabolic rate (71 min(-1) at 21% O(2), 53 min(-1) at 8%, 96 min(-1) at 4% and 64 min(-1) at 2%). Chlamydogobius eremius can use a buccal air bubble for aerial O(2) uptake, most probably in response to increased aquatic hypoxia. In air, C. eremius relies more on the buccal bubble as an oxygen source with increasing hypoxia up to an ambient O(2) of 4% (7.1% of V(O(2)) at 21% O(2); 14.5% at 8% O(2); and 27.1% at 4% O(2)), then when the available supply of O(2) is further reduced, it decreases (15% of V(O(2)) at 2% O(2)) and respiration across the skin again makes a higher relative contribution. The Australian desert goby has a higher metabolic rate in higher salinities (336 microl g(-1) h(-1) in 35 ppt, 426 microl g(-1) h(-1) in 70 ppt) than in freshwater (235 microl O(2) g(-1) h(-1)), presumably because of the increased metabolic cost of osmoregulation. There was no significant difference in V(O(2)) for fish in air that had come from varying salinities.     

On the function of female ornaments: male bluethroats prefer colourful females

Female ornaments in animals with conventional sex roles have traditionally been considered non-functional, being merely a genetically correlated response to selection for male ornamentation. Alternatively, female ornaments may be influenced by selection acting directly on the females, either through female–female competition or male choice. We tested the latter hypothesis in mate choice experiments with bluethroats (Luscinia s. svecica), a passerine bird in which females vary considerably in coloration of an ornamental throat patch. In outdoor aviaries placed in prime breeding habitat, males were allowed to choose between a colourful and a drab female. We found that males associated more with, and performed more sexual behaviours towards, colourful females. Female coloration was not age-related, but correlated significantly with body mass and tarsus length. Thus, we have demonstrated both a male preference for female ornamentation, and a relationship between ornament expression and female body size, which may be indicative of quality. Our results refute the correlated response hypothesis and support the hypothesis that female ornamentation is sexually selected.     

Do male house mice (Mus musculus) discriminate between females that differ in nutritional status?

Most studies of mate choice have focused on female preference for male traits because it is generally assumed that since males provide less parental investment they are not choosy. However, if males suffer missed opportunity costs by mating with lower quality females, selection should favor males with the ability to discriminate among females. We tested the hypothesis that male house mice (Mus musculus) discriminate between females that differ in nutritional status (non-food-deprived versus food-deprived). We recorded the time males spent investigating either type of female and used that to determine preference (spending ≥55% of their total investigation time with one female). We also examined the effects of female nutritional status and female preference status (preferred versus non-preferred) on the reproductive success of males. Males did not display a preference for non-food-deprived females nor did their reproductive success vary with nutritional status or preference status of females. Interestingly, males spent more time investigating females that were closest to the male's own weight. In addition, pairs that were closer in weight were more likely to produce a litter. These results suggest that male house mice are capable of discriminating among females and that such discrimination may influence their reproductive success.