Juvenile hormone and photoperiodically controlled polymorphism in Aphis fabae: Prenatal effects on presumptive oviparae

All three naturally occurring juvenile hormones (JH's) were shown to have effects on the parthenogenetic/gamic polymorphism of Aphis fabae; they mimicked long day conditions by inducing parthenogenetic forms. When topically applied to fourth instar gynoparae, JH caused the appearance of oviparous/viviparous intermediate morphs in the progeny. JH induced both wing development and embryogenesis in embryonic, presumptive oviparae. Embryogenesis was induced by lower doses of JH. Adult, embryo-containing alatae produced by treatment with high JH doses were capable of flight, and whilst reluctant to reproduce, their few viable progeny were oviparae. They did, however, differ from normal gynoparae in size, occasional presence of scent plaques on the metathoracic tibiae, numbers of secondary rhinaria on the antennae and morphogenetic response to postnatal rearing in long day conditions. The presumptive, oviparous embryos most sensitive to JH treatment were shown to be ca 323 μm in length, close to the stage where their germaria differentiate as parthenogenetic or gamic. Similar effects were observed in the progeny of JH-treated, teneral adult gynoparae but there was no effect on the morph of progeny of long day, alate virginoparae. The JH's differed in potency in the order JH I > JH II > JH III. The treatment of fourth instar gynoparae also induced a terminal batch of apparently normal viviparous progeny in a number of aphids. This result was obtained even at JH doses below threshold for the appearance of oviparous/viviparous intermorphs.     

Photoperiodic determination of the male and female sexual morphs of Myzus persicae

The chronology of the photoperiodic determination of sexual morphs in holocyclic Myzus persicae was studied in the laboratory by transfer of synchronized batches of aphids between long-day (16 hr) and short-day (10 hr) régimes at a constant temperature of 20°C. The length of exposure to the short-day régime was measured in terms of the number of long dark-periods received by the aphids. The photoperiodic response extended over four generations (P, G₁, G₂, and G₃ respectively). When P generation aphids were given short days from the fourth instar, alate viviparae and males appeared successively in generation G₂, oviparae in G₃. Increasing the number of long dark-periods received during the development of G₂ embryos had a cumulative effect on the number which developed into alate viviparae. Determination of all the first-born G₂ aphids as alatae occurred only if their mothers had been exposed to the short-day régime throughout larval development. Alate viviparae gave birth to oviparae if they received a minimum of 4 long dark-periods, starting from a late stage in their embryonic development. The critical stage for ovipara determination in the G₃ embryo was on the sixth or seventh day after ovulation, more than half-way through embryonic development. G₂ aphids were determined as males before ovulation if their parents received 4 (in some circumstances only 3) long dark-periods. In the clones studied, male determination, once initiated in the G₁ parent, could not be reversed by later back-transfer to the long-day régime.     

Juvenile hormone effects on polymorphism in the pea aphid, Acyrthosiphon pisum

When reared in short days (LD 12:12) at 15°C, apterous Acyrthosiphon pisum gave birth to sexual females (oviparae) exclusively for the first eight days of larviposition. After this time they switched to the production of parthenogenetic females (viviparae). Topical application of juvenile hormones I, II and III to fourth instar or adult ovipara-producers induced the precocious appearance of parthenogenetic females in the progeny sequence. Various forms intermediate between oviparae and viviparae were also produced and repetitive JH-I treatments resulted in a few alatiform progeny. However, many of the JH induced apterous, parthenogenetic females appeared to be normal viviparae and were capble of reproduction. Thus, prenatal treatment of oviparous embryos with JH diverts development towards the viviparous form. JH-I treatment of long-day reared A. pisum had no effect on the type of progeny produced.

---

Effets de l'hormone juvénile sur le polymorphisme d'Acythosiphon pisum

Résumé Quand il est élevé sous jours courts (LN 12/12) à 15°C, le type anglais vert d'Acyrthosiphon pisum ne donne naissance qu'à des femelles sexuées (ovipares) pendant la première partie de sa période de reproduction. Ensuite quelques types intermédiaires ovipares/vivipares peuvent apparaitre avant que les pucerons ne bifurquent spontanément vers la production de femelles parthénogénétiques (vivipares). L'application cutanée d'hormones juvéniles (JH I, II, et III) aux larves de quatrième stade ou à des adultes producteurs d'ovipares provoque l'apparition prématurée d'intermédiaires et de vivipares dans la descendance. Les différentes formes intermédiaires produites par des applications répétées de J.H. comprenaient des types ailés ou partiellement ailés. Cependant, les vivipares aptères induits par J.H. étaient morphologiquement normaux et beaucoup étaient capables de se reproduire. Des traitements semblables aux J.H. de vivipares élevées en jours longs (LN 16/8) n'ont pas eu d'effets sur le type de la descendance.On ne sait pas si l'action de JH exogène sur l'induction des vivipares est direct ou indirect. La reprogrammation des embryons, autrement destinés à se développer comme ovipares, est examinée en relation avec notre connaissance du contrôle endocrine du polymorphisme des pucerons.

     

Reproductive, morphological and behavioural affinities between the alate gynopara and virginopara of the aphid, Aphis fabae

ABSTRACT. 'Normal' alate virginoparae reared under long day conditions (LD 16:8) with postnatal crowding, and 'normal' gynoparae reared in un-crowded, short day conditions (LD 12:12) over two generations were compared in respect of the morph of the progeny, the frequency distribution of secondary rhinaria (placoid sensilla) on the third and fourth antennal segments, and preferred larviposition sites. Although in Aphis fabae the two morphs closely resemble one another morphologically, they differed in each of the above characters. Progeny sequences were analysed after transfer to the opposite photoperiodic regime at various times during postnatal development of the alate mothers. Transfer of presumptive gynoparae from short to long days induced the appearance of virginoparous progeny even when the transfer was made just after the final moult. Transfer of presumptive alate virginoparae from long to short days was effective in inducing oviparous offspring, only if the transfer was made during the first instar; oviparae were always first born. Intermediates between oviparae and viviparae were found at the time when the morph of the progeny changed. Transfer from long to short days also induced gynopara production but there appeared to be an intrinsic mechanism which prevented exclusive gynopara production by alates. When first instar, presumptive gynoparae were transferred to long days, the resulting adults would be described both reproductively and behaviourally as alate virginoparae; the opposite switch, of presumptive alate virginoparae to short days, resulted in adult gynoparae on the same criteria. However, the numbers of secondary rhinaria were influenced more by the prenatal than by the postnatal photoperiodic regime. There was an asymmetry of response in that a switch from short to long days had a greater effect on all three characters monitored than did the opposite switch from long to short days.     

Embryogenesis in parthenogenetic and sexual females of Aphis fabae

Embryogenesis and oogenesis in the black bean aphid, Aphis fabae, was studied by dissecting viviparous and oviparous individuals and examining whole mounts of the ovaries in Ringer's solution. Apteriform and alatiform virginoparae, gynoparae, and oviparae were raised on broadbean leafdiscs at 17.5° and either 16 h or 10 h light/day.Each of the two ovaries of these forms consists, with few exceptions, of six ovarioles. Development of embryos in virginoparous aphids can commence, in the most developed embryos within their grandmothers, but not before the latter reached the 4th instar. At birth viviparous larvae contain about two embryos in each ovariole. In apteriform larvae, additional embryos are generated at a rate of about one per instar. Adult apterae raised at 16 h and 10 h light/day contain about six and five embryos per ovariole, respectively. Alatiform larvae (virginoparae or gynoparae) raised under these conditions contain no more than four embryos per ovariole when they become adult. Ovulation in oviparae is evident only in the 2nd instar of these sexual females. Only one egg develops per ovariole during their larval development. A second egg occasionally develops later in the adult life of oviparae that have not mated and hence have not oviposited.

---

Zusammenfassung Die Embryogenese und Oogenese der Schwarzen Bohnenlaus, Aphis fabae, wurde untersucht durch Aufpräparieren von viviparen und oviparen Tieren und Überprüfung der Ovarien als Totalpräparate in Ringerlösung. Ungeflügelte und geflügelte Virginopare, Gynopare und Ovipate wurden an Blattscheibchen von Dicker Bohne bei 17,5° und 16/8 oder 10/14 HD gezogen.Jedes der beiden Ovarien dieser Formen besteht, mit wenigen Ausnahmen, aus sechs Ovariolen. Die Entwicklung der Embryonen von virginoparen Tieren kann bei den am weitesten entwickelten Embryonen in ihren Großmüttern beginnen aber nicht bevor die letzteren das 4. Larvenstadium erreicht haben. Bei der Geburt enthalten vivipare Larven etwa zwei Embryonen in jeder Ovariole. Bei apteriformen Larven entstehen weitere Embryonen mit einer Rate von etwa einem je Stadium. Adulte Ungeflügelte enthalten bei Aufzucht im 16/8 und im 10/14 HD-Tag etwa sechs bzw. fünf Embryonen je Ovariole. Alatiforme Larven (virginopare und gynopare) enthalten bei solchen Bedingungen nicht mehr als vier Embryonen je Ovariole, wenn sie adult werden. Die Ovulation ist bei den Oviparen erst im 2. Stadium dieser Sexualweibchen erkennbar. Nur ein Ei entwickelt sich je Ovariole während der Larvenentwicklung. Ein zweites Ei entwickelt sich gelegentlich später im adulten Leben von Oviparen, die sich nicht gepaart haben und demnach keine Eier abgelegt haben.

     

Composition of triglycerides from aphids of six different families and from different seasonal forms of Aphis evonymi

The triglyceride compositions of extracts and cornicle secretions of specimens from a range of aphid families were examined by mass spectrometry and found to support earlier evidence that there is little correlation between taxonomic position and chemical constitution.

Parasites developing within Myzus persicae preferentially consumed the typical aphid triglycerides which contain hexanoic (C₆), sorbic (C_6:2), myristic (C₁₄), and palmitic (C₁₆) acid moieties, so that when parasitism was advanced, only triglycerides with three long-chain fatty acids per molecule remained. The adult parasites themselves contained very little triglyceride.

Triglycerides of Aphis evonymi and Aphis fabae were similar and varied in composition regularly throughout the year. In the apterous and alate (summer) viviparae, there were equal amounts of myristoyl (C₁₄) and palmitoyl (C₁₆) triglycerides, while in fundatrices and fundatrigeniae (spring forms) myristoyl was predominant. Males collected in autumn resembled the spring forms. However, oviparae and eggs of these and other species differed considerably from the other seasonal forms, in having more hexenoic (C_6:1), sorbic (C_6:2), and myristoleic (C_14:1) acid moieties.     

Embryogenesis and oögenesis in alate virginoparae,gynoparae, and oviparae of the aphid Myzus persicae, in relation to photoperiod

The study reports on the effects of prenatal and/or postnatal exposures to short-night or long-night conditions, and of crowding, on embryogenesis and oögenesis in alate virginoparae, gynoparae, and oviparae of a holocyclic strain of the green peach aphid, Myzus persicae, from Yakima, Washington State.In alate virginoparae raised at a density of 10–20 per radish seedling in a short-night regime (8 hr darkness per diem), 3–4 embryos occurred in each of their 10 ovarioles, when the aphids attained adulthood. More than 30 larvae were deposited by most of these alatae. However, in young adult gynoparae, raised at these densities in a long-night regime (15 hr darkness per diem), only one viable embryo (a presumptive ovipara) occurred per ovariole. The follicle containing this embryo was followed by 1–2 abnormal follicles in each ovariole, and the number of larvae deposited by a gynopara was generally less than 10. In young adult oviparae similarly raised under a long-night regime, only one egg typically occurred in each of their 10 ovarioles, and the eggs deposited by an ovipara (only after it had mated) generally numbered less than 10. Alate virginoparae and gynoparae contained an additional embryo in some of their ovarioles when these morphs were raised at a lower density (1–5 per plant).Presumptive gynoparae partially developed the reproductive features of alate virginoparae when transferred to a short-night regime at birth; the converse was true when presumptive alate virginoparae were transferred to a long-night regime early in larval life. Oviparae maintained in short nights from before birth developed the appearance of apterous virginoparae but still produced eggs rather than embryos. However, their oögenesis was enhanced and eggs (10–20) were deposited by them without prior mating. Under all regimes tested, oviparae were always deposited early in the larviposition sequence of their alate mothers, and the number of oviparae deposited never exceeded 15.The possible involvement of juvenile hormone in the regulation of these events and the ecological significance of the results are discussed.     

Induced life cycle transition from holocycly to anholocycly of the Russian wheat aphid (Homoptera: Aphididae)

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko),exists with holocyclic life cycle in Tacheng, Xinjiang in Northwest China. It produces males and oviparae to mate and oviposit for overwintering by eggs. Under laboratory conditions with 14 h/d photophase and temperature not lower than 15℃, RWA occurred in parthenogenesis and produced no males. The laboratory popu-lations of Russian wheat aphid, which were kept under natural conditions in fall by 15th, 49th and 81st generation while wild populations produced males and oviparae for mating, produced males and oviparae with their number decreased gradually, but viviparae and nymphs increased sequen-tially. As a result, it produced a small amount of oviparae and no males emerged in fields by 49 generations' reproduction in laboratory. After development of 81 generations, oviparae happened occasionally and no eggs occurred for overwintering instead of viviparae and nymphs. A hypothesis of RWA disastrous process was proposed. The life cycle of RWA can be changed from holocycly to anholocycly in its long-term spread and evolution. Anholocycly is more dangerous than holocycly to small grains for its strong adaptability and dispersal ability.     

Production of males and gynoparae by apterous viviparae of Myzus persicae continuously exposed to different scotoperiods

At 18–19°C, apterous viviparae of a holocyclic strain of Myzus persicae raised from birth under constant scotoperiods of 9 hr 26 min–15 hr darkness per diem deposited apterous viviparae, alate viviparae, and males, in that sequence. Under the shortest scotoperiod (9 hr 26 min) in which males were recorded, only a few were deposited at the end of reproduction. With increasing duration of the scotoperiods, the aphids switched to the exclusive deposition of males progressively earlier in their reproductive lives. Thus more males and fewer females were produced; however the proportion of wingless females increased. Similar trends were recorded when the number of prenatal exposures to each scotoperiod was increased from 0 to 7.Alatae developed into gynoparae at scotoperiods of 10 hr 29 min or longer, and into virginoparae at 9 hr 40 min or shorter scotoperiods. Gynoparae and alate virginoparae, as well as alates that produced both oviparae and viviparae were found at 10 hr and 10 hr 15 min.When apterous viviparae were transferred to scotoperiods of 10 hr 29 min or 15 hr only when they attained adulthood, they also deposited males but only toward the end of their reproductive lives.     

The ovaries of aphids (Hemiptera,Sternorrhyncha, Aphidoidea): morphology and phylogenetic implications

The ovaries of aphids belonging to the families Eriosomatidae, Anoeciidae, Drepanosiphidae, Thelaxidae, Aphididae, and Lachnidae were examined at the ultrastructural level. The ovaries of these aphids are composed of several telotrophic ovarioles. The individual ovariole is differentiated into a terminal filament, tropharium, vitellarium, and pedicel (ovariolar stalk). Terminal filaments of all ovarioles join together into the suspensory ligament, which attaches the ovary to the lobe of the fat body. The tropharium houses individual trophocytes and early previtellogenic oocytes termed arrested oocytes. Trophocytes are connected with the central part of the tropharium, the trophic core, by means of broad cytoplasmic processes. One or more oocytes develop in the vitellarium. Oocytes are surrounded by a single layer of follicular cells, which do not diversify into distinct subpopulations. The general organization of the ovaries in oviparous females is similar to that of the ovaries in viviparous females, but there are significant differences in their functioning: (1) in viviparous females, all ovarioles develop, whereas in oviparous females, some of them degenerate; (2) the number of germ cells per ovariole is usually greater in females of the oviparous generation than in females of viviparous generations; (3) in oviparous females, oocytes in the vitellarium develop through three stages (previtellogenesis, vitellogenesis, and choriogenesis), whereas in viviparous females, the development of oocytes stops after previtellogenesis; and (4) in the oocyte cytoplasm of oviparous females, lipid droplets and yolk granules accumulate, whereas in viviparous females, oocytes accrue only lipid droplets. Our results indicate that a large number of germ cells per ovariole represent the ancestral state within aphids. This trait may be helpful in inferring the phylogeny of Aphidoidea.     

Germ cell cluster formation and ovariole structure in viviparous and oviparous generations of the aphid Stomaphis quercus

The developing ovaries of S. quercus contain a limited number of oogonial cells which undergo a series of incomplete mitotic divisions resulting in the formation of clusters of cystocytes. Ovaries of viviparous generations contain 6 to 9 clusters, containing 32 cystocytes each, whereas ovaries of oviparous generations contain 5 clusters containing 45-60 cystocytes. During further development, clusters become surrounded by a single layer of follicular cells, and within each cluster the cystocytes differentiate into oocytes and trophocytes (nurse cells). Concurrently, cysts transform into ovarioles. The anterior part of the ovariole containing the trophocytes becomes the tropharium, whereas its posterior part containing oocytes transforms into the vitellarium. The vitellaria of viviparous females are composed of one or two oocytes, which develop until previtellogenesis. The nuclei of previtellogenic oocytes enter cycles of mitotic divisions which lead to the formation of the embryo. Ovarioles of oviparous females contain a single oocyte which develops through three stages: previtellogenesis, vitellogenesis and choriogenesis. The ovaries are accompanied by large cells termed bacteriocytes which harbor endosymbiotic microorganisms.     

Induced life cycle transition from holocycly to anholocycly of the Russian wheat aphid (Homoptera: Aphididae)

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), exists with holocyclic life cycle in Tacheng, Xinjiang in Northwest China. It produces males and oviparae to mate and oviposit for overwintering by eggs. Under laboratory conditions with 14 h/d photophase and temperature not lower than 15℃, RWA occurred in parthenogenesis and produced no males. The laboratory populations of Russian wheat aphid, which were kept under natural conditions in fall by 15th, 49th and 81st generation while wild populations produced males and oviparae for mating, produced males and oviparae with their number decreased gradually, but viviparae and nymphs increased sequentially. As a result, it produced a small amount of oviparae and no males emerged in fields by 49 generations' reproduction in laboratory. After development of 81 generations, oviparae happened occasionally and no eggs occurred for overwintering instead of viviparae and nymphs. A hypothesis of RWA disastrous process was proposed. The life cycle of RWA can     

Seasonal shifts along the oviparity–viviparity continuum in a cold‐climate lizard population

Squamate embryos require weeks of high temperature to complete development, with the result that cool climatic areas are dominated by viviparous taxa (in which gravid females can sun‐bask to keep embryos warm) rather than oviparous taxa (which rely on warm soil to incubate their eggs). How, then, can some oviparous taxa reproduce successfully in cool climates – especially late in summer, when soil temperatures are falling? Near the northern limit of their distribution (in Sweden), sand lizards (Lacerta agilis) shift tactics seasonally, such that the eggs in late clutches complete development more quickly (when incubated at a standard temperature) than do those of early clutches. That acceleration is achieved by a reduction in egg size and by an increase in the duration of uterine retention of eggs (especially, after cool weather). Our results clarify the ability of oviparous reptiles to reproduce successfully in cool climates and suggest a novel advantage to reptilian viviparity in such conditions: by maintaining high body temperatures, viviparous females may escape the need to reduce offspring size in late‐season litters.     

Variation in eggshell characteristics and in intrauterine egg retention between two oviparous clades of the lizard Lacerta vivipara: insight into the oviparity-viviparity continuum in squamates

The concept of the oviparity-viviparity continuum refers to the wide range in the length of intrauterine egg retention and, hence, in the stage of embryonic development at oviposition existing in squamates. The evolutionary process underlying this continuum may involve not only a lengthening of egg retention in utero, but also a marked reduction in the thickness of the eggshell. The idea that there may exist a negative correlation between the developmental stage reached by the embryo at oviposition and the eggshell thickness within squamates, although supported by the comparison of oviparous vs. viviparous species, has seldom been evaluated by comparing eggshell thickness of oviparous forms with different lengths of intrauterine egg retention. Eggs of two distinct oviparous clades of the lizard Lacerta vivipara were compared. The eggs laid by females from Slovenian and Italian populations have thicker eggshells, contain embryos on average less developed at the time of oviposition, and require a longer incubation period before hatching than the eggs laid by females from French oviparous populations. Our data and several other examples available from the literature support the idea that the lengthening of intrauterine retention of eggs and the shortening of the subsequent external incubation of eggs are associated with reduction in the thickness of the eggshell, at least in some lineages of oviparous squamates. The current hypotheses that may account for this correlation are presented and a few restrictions and refinements to those hypotheses are discussed. In particular, other changes, such as increased vascularization of the oviduct and of the extraembryonic membranes, may play the same role as the decrease of eggshell thickness in facilitating prolonged intrauterine egg retention in squamates. Future studies should also consider the hypothesis that the length of intrauterine retention might directly depend on the extent of maternal-fetal chemical communication through the eggshell barrier.     

Revisionary notes on the genus Metopolophium Mordvilko, 1914, with keys to European species and descriptions of two new taxa (Homoptera: Aphidoidea)

New and extensively revised keys are given to help identification of the European species of Metopolophium Mordvilko, 1914. The morphs keyed are (1) the apterous viviparous females from Gramineac, (2) the alate viviparous females and (3) the males and oviparous females of those species that overwinter as eggs on Rosa spp. Taxonomic notes are given on some individual species. Two new taxa, M. fasciatum sp. nov., and M. festucae (Theobald) cerealium subsp. nov. are described. Metopolophium myrmecophilum (Theobald) becomes a new synonym of M. festucae (Theobald), sensu stricto , and the resulting question of the possible conservation of the latter, which is the junior subjective synonym, is discussed. A revised checklist of the European species of Metopolophium is given.     

Comparison of ovarian functions for keeping embryos by measurement of dissolved oxygen concentrations in ovaries of copulatory and non-copulatory oviparous fishes and viviparous fishes

To investigate causes of anomalous development of embryos facultatively fertilized in the ovary of a non-copulatory oviparous fish Hemilepidotus gilberti (Scorpaeniformes: Cottdae), dissolved oxygen (DO) concentrations were measured in ovaries of copulatory oviparous (Alcichthys alcicornis, Bero elegans), non-copulatory oviparous (H. gilberti, Hexagrammus otakii), and viviparous (Sebastes taczanowskii, Zoarces elongatus) fishes. DO concentrations changed during vitellogenesis and ovulation cycles, and also before and after ovulation. DO concentrations in the ovary of H. gilberti and H. otakii at ovulation were 0.27±0.03 and 0.15±0.03 mg O₂ l⁻¹, respectively, whereas in A. alcicornis and B. elegans, the concentrations were 0.47±0.08 and 0.20±0.06 mg O₂ l⁻¹, respectively. In the ovaries of intralumenal gestation viviparous fishes, S. taczanowskii and Z. elongatus, DO concentration was from 0.01 to 0.11 mg O₂ l⁻¹. The average DO concentration during the artificial pregnancy of A. alcicornis was 0.97±0.19 mg O₂ l⁻¹, but all embryos showed deformity. DO concentrations recorded in oviparous fishes in this study were lower than the oxygen level at which most oviparous fish embryos exhibit retardation or death, and it probably caused the anomalous embryonic development. In contrast, the normal development of viviparous fish embryos at low oxygen level was attributed to the specialized structure of ovary, e.g. the dual arterial system to supply the developing embryos with the respiratory demands in Sebastes.     

Juvenile hormone and methyl farnesoate production in cockroach embryos in relation to dorsal closure and the reproductive modes of different species of cockroaches

Juvenile hormone (JH), produced by the corpora allata (CA), is first detectable after dorsal closure, a conspicuous event in embryogenesis. The present research found that the timing of dorsal closure was consistently at about 45% of the total embryonic development time across most of the oviparous and ovoviviparous cockroach species examined. These included the ovoviviparous cockroaches Blaberus discoidalis, Byrsotria fumigata, Rhyparobia maderae, Nauphoeta cinerea, Phoetalia pallida, Schultesia lampyridiformis, and Panchlora nivea, as well as the oviparous cockroaches Blatta orientalis, Periplaneta americana, Eurycotis floridana, and Supella longipalpa. However, the only known viviparous cockroach Diploptera punctata completed dorsal closure at 20.8% of embryo development time. Methyl farnesoate (MF), the immediate precursor of JH III, is considered a functional molecule in crustaceans; however, in insects its function is still unclear. To understand the role of JH and MF in cockroach embryos, I compared JH and MF biosynthesis and release in several cockroach species of known phylogenetic relationships. Using a radiochemical assay, the present research showed that cockroach embryos representing all three reproductive modes produced and released both JH and MF, as previously shown for B. germanica, N. cinerea, and D. punctata. Members of a pair of embryonic CA from B. discoidalis, B. fumigata, R. maderae, and D. punctata were incubated with and without farnesol. MF accumulated in large amounts only in CA of R. maderae in the presence of farnesol, which indicates that control of the last step of biosynthesis of JH, conversion of MF into JH by MF epoxidase, is probably a rate-limiting step in this species.     

Is increased maternal basking an adaptation or a pre-adaptation to viviparity in lizards?

Pregnant females modify their thermoregulatory behaviour in many species of viviparous (live-bearing) reptiles, typically maintaining higher and more stable body temperatures at this time. Such modifications often have been interpreted as adaptations to viviparity, functioning to accelerate embryonic development and/or modify phenotypic traits of hatchlings. An alternative possibility is that similar maternal thermophily may be widespread also in oviparous species and if so, would be a pre-adaptation (rather than an adaptation) to viviparity. Because eggs are retained in utero for a significant proportion of development even in oviparous reptiles, maternal thermophily might confer similar advantages in oviparous as in viviparous taxa. Experimental trials on montane oviparous scincid lizards (Bassiana duperreyi) support the pre-adaptation hypothesis. First, captive females (both reproductive and non-reproductive) selected higher temperatures than males. Second, experimentally imposing thermal regimes on pregnant females significantly affected their oviposition dates and the phenotypic traits (body shape, running speed) of their hatchlings. Thus, as for many other behavioural correlates of pregnancy in viviparous reptiles, maternal thermophily likely may have already been present in the ancestral oviparous taxa that gave rise to present-day viviparous forms.