Effects of food deprivation on plasma insulin-like growth factor-1 (Igf1) and Igf binding protein (Igfbp) gene transcription in juvenile cabezon (Scorpaenichthys marmoratus).

The growth hormone (GH)/insulin-like growth factor (Igf) endocrine axis regulates somatic growth in the face of changing environmental conditions. In actinopterygian fishes, food availability is a key modulator of the somatotropic axis, with lower food intake generally depressing liver Igf1 release to diminish growth. Igf1 signaling, however, also involves several distinct IGF binding proteins (Igfbps), and the functional roles of many of these Igfbps in affecting growth during shifting food availability remain uncertain. Here, we tested how complete food deprivation (fasting) affected gene transcription for paralogs of all six types of Igfbps in the liver and fast-twitch skeletal muscle of cabezon (Scorpaenichthys marmoratus), a nearshore marine fish important for recreational fisheries in the eastern North Pacific Ocean. Juvenile cabezon were maintained as either fed (6% mass food⋅g fish wet mass-1⋅d-1) or fasted for 14 d. Fasted fish exhibited a lower body condition (K), a depressed mass-specific growth rate (SGR), and reduced plasma concentrations of Igf1. In the liver, fasting reduced the relative abundance of gene transcripts encoding Igfbps igfbp2a and igfbp2b, while significantly elevating mRNA levels for igfbp1a, igfbp1b, igfbp3b, and igfbp4. Fasting also reduced hepatic mRNA levels of GH receptor-1 (ghr1) - but not GH receptor-2 (ghr2) - supporting the idea that changes in liver sensitivity to GH may underlie the decline in plasma Igf1 during food deprivation. In skeletal muscle, fasting downregulated gene transcripts encoding igf1, igfbp2b, igfbp5b, and igfbp6b, while also upregulating mRNAs for igf2 and ghr2. These data demonstrate isoform-specific regulation of Igfbps in liver and skeletal muscle in cabezon experiencing food deprivation and reinforce the idea that the repertoire of duplicated Igfbp genes that evolved in actinopterygian fishes supports a diverse scope of endocrine and paracrine functions.

Interactions of long-term food ration variation and short-term fasting on insulin-like growth factor-1 (IGF-1) pathways in copper rockfish (Sebastes caurinus).

Variation in food intake affects somatic growth by altering the expression of hormones in the somatotropic endocrine axis including insulin-like growth factor-1 (IGF-1). Here, we examined IGF-1 pathway responses to long- and short-term variation in food availability in copper rockfish (Sebastes caurinus), a nearshore Pacific rockfish important for commercial and recreational fisheries. Juvenile copper rockfish were raised under differing ration amounts (3% or 9% mass feed·g-1 fish wet mass·day-1) for 140 d to simulate 'long-term' feeding variation, after which some fish from both rations were fasted for 12 d to generate 'short-term' conditions of food deprivation. Rockfish on the 9% ration treatment grew more quickly than those on the 3% ration and were larger in mass, length, and body condition (k) after 152 d. Fish on the 9% ration had higher blood glucose than those on the 3% ration, with fasting decreasing blood glucose in both ration treatments, indicating that both long-term and short-term feed treatments altered energy status. Plasma IGF-1 was higher in rockfish from the 9% ration than those in the 3% ration and was also higher in fed fish than fasted fish. Additionally, plasma IGF-1 related positively to individual variation in specific growth rate (SGR). The positive association between IGF-1 and SGR showed discordance in fish that had experienced different levels of food and growth over the long-term but not short-term, suggesting that long-term nutritional experience can influence the relationship between IGF-1 and growth in this species. Rockfish on the 3% ration showed a lower relative abundance of gene transcripts encoding igf1 in the liver, but higher hepatic mRNAs for IGF binding proteins igfbp1a and igfbp1b. Fasting similarly decreased the abundance of igf1 mRNAs in the liver of fish reared under both the 9% and 3% rations, while concurrently increasing mRNAs encoding the IGF binding proteins igfbp1a, -1b, and -3a. Hepatic mRNAs for igfbp2b, -5a, and -5b were lower with long-term ration variation (3% ration) and fasting. Fish that experienced long-term reduced rations also had higher mRNA levels for igfbp3a, -3b, and IGF receptors isoforms A (igf1rA) and B (igf1rB) in skeletal muscle, but lower mRNA levels for igf1. Fasting increased muscle mRNA abundance for igfbp3a, igf1rA, and igf1rB, and decreased levels for igfbp2a and igf1. These data show that a positive relationship between circulating IGF-1 and individual growth rate is maintained in copper rockfish even when that growth variation relates to differences in food consumption across varying time scales, but that long- and short-term variation in food quantity can shift basal concentrations of circulating IGF-1 in this species.

Response of the insulin-like growth factor-1 (Igf1) system to nutritional status and growth rate variation in olive rockfish (Sebastes serranoides).

Growth performance in vertebrates is regulated by environmental factors including the quality and quantity of food, which influence growth via endocrine pathways such as the growth hormone (GH)/insulin-like growth factor somatotropic axis. In several teleost fishes, circulating concentrations of insulin-like growth factor-1 (Igf1) correlate positively with growth rate, and it has been proposed that plasma Igf1 levels may serve as an indicator of growth variation for fisheries and aquaculture applications. This study tested whether plasma Igf1 concentrations might serve as an indicator of somatic growth in olive rockfish (Sebastes serranoides), one species among dozens of rockfishes important to commercial and recreational fisheries in the Northern Pacific Ocean. Juvenile olive rockfish were reared under food ration treatments of 1% or 4% wet mass per d for 98 d to experimentally generate variation in growth. Juvenile rockfish in the 4% ration grew 60% more quickly in mass and 22% faster in length than fish in the 1% ration. Plasma Igf1 levels were elevated in rockfish under the 4% ration, and individual Igf1 levels correlated positively with growth rate, as well as with individual variation in hepatic igf1 mRNA levels. Transcripts encoding the Igf binding proteins (Igfbps) igfbp1a and igfbp1b were also at higher abundance in the liver of rockfish in the 1% ration treatment, while mRNAs for igfbp5a and igfbp5b were elevated in the skeletal muscle of 4% ration fish. These findings support the use of plasma Igf1 as a physiological index of growth rate variation in rockfish.

Big wigs and small wigs: Time, sex, size and shelter affect cohabitation in the maritime earwig (Anisolabis maritima).

Animal aggregations can occur for a variety of abiotic factors, such as resource limitation, or biotic factors, including group foraging and protection from predators. In our study, we examined whether time, sex, body size or shelter availability affected aggregation behavior of the maritime earwig, Anisolabis maritima (Order Dermaptera), an insect found globally at high densities under driftwood. Specifically, we monitored the distribution of two individuals in arenas with either two shelters (no habitat limitation) or one shelter (habitat limitation) to determine their propensity for cohabitation at times of peak activity and times of quiescence. Females, whose high levels of aggression are often associated with maternal care, were particularly averse to cohabitation, whereas males were generally more tolerant of other earwigs. Females initially preferred not to cohabitate when placed with a male, but were more tolerant of cohabitation later, regardless of the number of shelters. Same-sex pairs, on the other hand, were less likely to cohabitate with only one shelter present, but males were again more tolerant of conspecifics than females regardless of habitat limitation. When competition for one shelter did not lead to cohabitation, the lone occupant was more likely to be the larger individual in same-sex trials and females in mixed-sex trials. Understanding the tolerance for close proximity under these varying conditions may provide insight into aggregative behavior and spatial distribution patterns in the maritime earwig.