Developmental asynchrony and host species identity predict variability in nestling growth of an obligate brood parasite: a test of the “growth-tuning” hypothesis

Generalist obligate brood parasites are excellent models for studies of developmental plasticity, as they experience a range of social and environmental variation when raised by one of their many hosts. Parasitic Brown-headed Cowbirds (Molothrus ater (Boddaert, 1783)) exhibit host-specific growth rates, yet cowbird growth rates are not predicted by hosts’ incubation or brooding periods. We tested the novel “growth-tuning” hypothesis which predicts that total asynchrony between cowbirds’ and hosts’ nesting periods results in faster parasitic growth in nests where host young fledge earlier than cowbirds. We tested this prediction using previously-published and newly-added nestling mass data across diverse host species. Total nesting period asynchrony (summed across incubation and brooding stages) predicted cowbird growth; 8-day old cowbirds were heavier in host nests with relatively shorter nesting periods. We further explored the drivers of variation in growth using mass measurements of cowbirds in Song Sparrow (Melospiza melodia (Wilson, 1810)) and Red-winged Blackbird (Agelaius phoeniceus (Linnaeus, 1766)) nests. Our top models included host species (cowbirds grew faster in sparrow nests), numbers of nestmates (slowest when raised alone), and sex (males grew faster). These results confirm that multiple social and environmental factors predict directional patterns of developmental plasticity in avian generalist brood parasites.

Transcriptome profiling reveals exposure to predicted end-of-century ocean acidification as a stealth stressor for Atlantic cod larvae

Ocean acidification (OA), a direct consequence of increasing atmospheric CO2 concentration dissolving in ocean waters, is impacting many fish species. Little is known about the molecular mechanisms underlying the observed physiological impacts in fish. We used RNAseq to characterize the transcriptome of 3 different larval stages of Atlantic cod (Gadus morhua) exposed to simulated OA at levels (1179 µatm CO2) representing end-of-century predictions compared to controls (503 µatm CO2), which were shown to induce tissue damage and elevated mortality in G. morhua. Only few genes were differentially expressed in 6 and 13 days-post-hatching (dph) (3 and 16 genes, respectively), during a period when maximal mortality as a response to elevated pCO2 occurred. At 36 dph, 1413 genes were differentially expressed, most likely caused by developmental asynchrony between the treatment groups, with individuals under OA growing faster. A target gene analysis revealed only few genes of the universal and well-defined cellular stress response to be differentially expressed. We thus suggest that predicted ocean acidification levels constitute a “stealth stress” for early Atlantic cod larvae, with a rapid breakdown of cellular homeostasis leading to organismal death that was missed even with an 8-fold replication implemented in this study.

Arrangement and size variation of intra-gonadal offspring in a viviparous asterinid sea star

Sibling competition and developmental asynchrony may greatly influence the arrangement and size of offspring of marine invertebrates that care for their young. In Parvulastra parvivipara, an asterinid sea star that incubates its young in the gonads, sibling cannibalism supports post-metamorphic development. Offspring size varies within (coefficient of variation, CV = 22.6 %) and among (CV = 17.7%) the gonads. Confocal microscopy was used to visualize early embryos and oocytes, and revealed the presence of several developmental stages within individual gonads. The eggs were a mean diameter of 84 μm. The observation of a gastrula at 86 µm smaller than the largest egg observed (134 µm) suggests that terminal egg size varies. The appearance of early embryos surrounded by somatic cells suggests that they may receive nutrients through histotrophy. Sibling competition intensifies once the digestive tract is functional in the tiny juveniles which then start to consume siblings. The arrangement of the offspring in the gonads was observed using micro-computed tomography. The juveniles were oriented with their oral surface facing each other, presumably as a defensive strategy to protect themselves from being eaten. Periodic release of offspring in single or several cohorts indicates continual reproduction. Released and retained juveniles varied in size. It is not known what initiates birth but it may be mediated by sibling competition. Larger adults had a greater allocation to female reproductive output than smaller adults.

Behavioral Profiles of Clinically Referred Children with Intellectual Giftedness

It is common that intellectually gifted children—that is, children with an IQ ≥ 130—are referred to paediatric or child neuropsychiatry clinics for socio-emotional problems and/or school underachievement or maladjustment. These clinically-referred children with intellectual giftedness are thought to typically display internalizing problems (i.e., self-focused problems reflecting overcontrol of emotion and behavior), and to be more behaviorally impaired when “highly” gifted (IQ ≥ 145) or displaying developmental asynchrony (i.e., a heterogeneous developmental pattern, reflected in a significant verbal-performance discrepancy on IQ tests). We tested all these assumptions in 143 clinically-referred gifted children aged 8 to 12, using Wechsler’s intelligence profile and the Child Behavior Checklist. Compared to a normative sample, gifted children displayed increased behavioral problems in the whole symptomatic range. Internalizing problems did not predominate over externalizing ones (i.e., acted-out problems, reflecting undercontrol of emotion and behavior), revealing a symptomatic nature of behavioral syndromes more severe than expected. “Highly gifted” children did not display more behavioral problems than the “low gifted.” Gifted children with a significant verbal-performance discrepancy displayed more externalizing problems and mixed behavioral syndromes than gifted children without such a discrepancy. These results suggest that developmental asynchrony matters when examining emotional and behavioral problems in gifted children.

Larval morphology and ontogeny of Nasikabatrachus sahyadrensis Biju & Bossuyt, 2003 (Anura, Nasikabatrachidae) from Western Ghats, India

The external, oral and buccopharyngeal morphologies of Nasikabatrachus sahyadrensis tadpoles were studied using ste-reoscopic and scanning electron microscopy. Using DNA barcodes, taxonomic identity of the tadpoles was establishedand tadoples of N. sahyadrensis were reared in semi-natural conditions. Development in the species from hatching tometamorph was prolonged and it took about 100 days for the freshly hatched larvae to metamorphose. The tadpoles areexotrophic, torrent dwelling with a large ventral suctorial oral disc, broadly rounded snout, cylindrical body, and a funnelshaped vent tube opening medially. During development external and buccopharyngeal characters show extensive changes. During metamorphosis developmental asynchrony was observed.

Embryonic communication in the nest: metabolic responses of reptilian embryos to developmental rates of siblings

Incubation temperature affects developmental rates and defines many phenotypes and fitness characteristics of reptilian embryos. In turtles, eggs are deposited in layers within the nest, such that thermal gradients create independent developmental conditions for each egg. Despite differences in developmental rate, several studies have revealed unexpected synchronicity in hatching, however, the mechanisms through which synchrony are achieved may be different between species. Here, we examine the phenomenon of synchronous hatching in turtles by assessing proximate mechanisms in an Australian freshwater turtle ( Emydura macquarii ). We tested whether embryos hatch prematurely or developmentally compensate in response to more advanced embryos in a clutch. We established developmental asynchrony within a clutch of turtle eggs and assessed both metabolic and heart rates throughout incubation in constant and fluctuating temperatures. Turtles appeared to hatch at similar developmental stages, with less-developed embryos in experimental groups responding to the presence of more developed eggs in a clutch by increasing both metabolic and heart rates. Early hatching did not appear to reduce neuromuscular ability at hatching. These results support developmental adjustment mechanisms of the ‘catch-up hypothesis’ for synchronous hatching in E. macquarii and implies some level of embryo–embryo communication. The group environment of a nest strongly supports the development of adaptive communication mechanisms between siblings and the evolution of environmentally cued hatching.