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Eulimnogammarus etingovae sp. nov. (Fig. 1A, Fig. 2) Holotype: female, body length 11 mm. South Baikal, near Kultuk, 51.696N, 103.874E, depth 10–20 m, dredge on sandy substrate, August 2013. Numerous paratypes of both sexes, same location and date. Holotype location: Zoological Museum, Moscow State University, Moscow, Russia. Paratypes: ETSU museum of Natural History, Johnson City, TN, USA and Baikal Museum, Listvyanka, Russia. See Supplementary materials for holotype museum ID. Etymology. The species is named after Anna Etingova who participated in the collection of the holotypes. Diagnosis. The species can be distinguished from other Eulimnogammarus spp. by a 1-articulate accessory flagellum, sparse setation on rami of uropod III, lack of calceoli, lack of setae on uropods I and II and of plumose setae on uropod III and presence of spines only on the last two body segments. Description. Description is based on female holotype and two male paratypes. No sexual dimorphism noted other than the presence of brood chamber in females and slightly weaker gnathopods I in female. Body slender, smooth, 8–11 mm, red when alive, with yellow spots on the posterior half of the head segment. Small spines on the last two segments of the urosome, setae on the last segment of pleosome and the first segment of urosome. Eyes kidney-shaped, white with black spots (black in preserved material). Rostrum very short, rounded, antennal sinus shallow (Fig. 1A). Antennae I short (1/4 body length) with the first peduncle article about 2/3 as long as the head segment and the length ratio of peduncle segments 1:0.6:0.4, carrying small setae on the distal end of each segment of peduncle and main flagellum. Flagellum consists of 9-12 articles. Accessory flagellum 1-articulate, very short, often barely visible (Fig. 2A). Antennae II shorter than I, peduncle articles carrying rare single setae, flagellum consists of 6 articles carrying short setae. No calceoli found (Fig. 2B). Mouthparts typical for subgenus Eurybiogammarus (Bazikalova 1945). Basal article of mandible palpus with- out setae, terminal article slightly shorter than the subterminal one; the comb is much shorter than the apical setae (Fig. 2C). Outer plate of maxillae I carries hooks with up to 5 teeth, inner plate triangle with dense pennate setae (Fig. 2D). Maxillae II (Fig. 2E) and maxillipedae (Fig. 2F) as in any Eulimnogammarus spp. Gnathopods I with weak, almond-shaped, weakly setose propodus with 8 pairs of spines on posterior margin (Fig. 2G), and with a group of weak setae at the base of the dactylus, somewhat more powerful in males. Gnathopods II with even weaker, heavily setose subrectangular elongated propodus with oblique palmar edge and a group of spines at the palmar-posterior corner (Fig. 2H). Pereopods short, stalky, with short spines and few setae, coxal plates short, rounded, with short setae on the posterior edge. Basipodite of pereopode VII with a large, round lobe extending distally in a rounded protrusion that reaches to the distal end of the next segment (Fig. 2I). Posterior edge serrated, with a weak seta under each notch. Uropods I and II with spines. Pleopods of typical gammarid morphology, with 2 small (50 microns) retinacles on the basal article, each equipped with 4-5 bumps on the convex side and 1-2 hooks on the concave side. Uropod III elongated, nearly bare, peduncle with 2 groups of 3-4 spines, outer ramus 2-2.5 times longer than the peduncle, 2-articulate, with 3 short spine and 1-3 weak simple setae on the outer margin, no spines or setae on the inner margin, 4-5 spines and a few setae at the distal end, spines reaching to ½ of the length of the triangle 2 nd article (Fig. 2J). Inner ramus narrow, about 2/3 as long as the outer ramus, narrow and slightly curved, completely bare, except for 1 spine and 2-3 setae at the distal end. Telson cleft to the base with 1-3 short spines at the tip of branches (Fig. 2K). Remarks: this species shares morphological affinities with both Echiuropus (1-articulate accessory flagellum, sparse to no setation on rami of uropod III) and Eulimnogammarus (2-articulate outer ramus of uropod III). It is similar to Eulimnogammarus aheneus and Eulimnogammarus similis, but it has neither calceoli, nor setae on uropods I and II nor plumose setae on uropod III. Similar to E. hyacynthus, but is smaller, red rather than blue and has spines only on the last two body segments. Differs from all other Eulimnogammarus spp. except the next species by having a 1-articulate accessory flagellum and by the structure of uropod III. Molecular phylogeny places this species basally within the paraphyletic genus Eulimnogammarus, with possible affinities to either the genus Macropereiopus which clusters within Eulimnogammarus (Naumenko et al. 2017; Fig. 5 below), or to the Echiuropus which is basal to Baikal clade 2 (Naumenko et al. 2017; Supplementary Fig. 1), depending on the nucleotide vs. amino acid sequences of the protein coding genes analyzed. This species is different from the next one by weak gnathopods, inner branch of uropod III longer than 2/3 of the outer branch, no setation on antennae II, uropod III and telson and a more protruding distal lobe on pereopod VII basipodite.

Eulimnogammarus tchernykhi sp. nov. (Fig. 1B, Fig. 3) Holotype: female, body length 8 mm, Baikal, Bolshoy Ushkanii Island, Pescherka bay, 53.852N, 108.660E, depth 15–20 m, dredge on sandy substrate with pebbles, August 2013. 2 paratypes (1 male, 1 female), same location and date. Holotype location: Zoological Museum, Moscow State University, Moscow, Russia. Paratypes: Department of Biological sciences, East Tennessee State Universiry, Johnson City, TN, USA and Baikal Museum, Listvyanka, Russia. See Supplementary materials for holotype museum ID. Etymology: The species is named after Valery Chernykh who participated in the collection of the holotypes. Diagnosis: This species can be distinguished from other Eulimnogammarus spp. by 1- or 2-articulate accessory flagellum, lack of calceoli, a single pair of spines only on the last 2 segments of urosome and dense setation of outer ramus and strong spines on peduncle of uropod III. Description: Description is based on female holotype and two male paratypes. No sexual dimorphism noted other than the presence of brood chamber in females. Body compact, smooth, 6-10 mm, red when alive, with crosshatching on the head segment. Two strong spines on the last two segments of the urosome, bundles of setae on the last segment of pleosome and all segment of urosome, individual setae on the 2 nd segment of pleosome. Eyes kidney-shaped, black. Rostrum very short, rounded, antennal sinus deeply cut (Fig. 1B). Antennae I short (1/3 body length) with the first peduncle article about 1/2 as long as the head segment and the length ratio of peduncle segments 1:0.8:0.6, carrying a few setae on the distal end of each peduncle segment. Flagellum consists of 12–15 articles (Fig. 3A). Accessory flagellum 1-articulate (in holotype female and several paratype males, sometimes 2-articulate (in two paratype males), in this case the second article is very short, 1/10 of the length of the terminal setae of the 1 st article. Antennae II ¾ as long as antennae I, peduncle and flagellum segments with groups of long setae on ventral side, flagellum consists of 6 articles. No calceoli found (Fig. 3B). Mouthparts typical for subgenus Philolimnogammarus (sensu Bazikalova 1945). Basal article of mandible palpus without setae, terminal article slightly shorter than the subterminal one; the comb consists of two rows of spines and is much shorter than the apical setae (Fig. 3C). Outer plate of maxillae I carries hooks with 6-7 short dense teeth, inner plate triangle with dense pennate setae (Fig. 3D). Maxillae II (Fig. 3E) and maxillipedae (Fig. 3F) as in any Eulimnogammarus spp. Gnathopods I with very strong and powerful almond-shaped propodus with 4–5 strong spines on posterior margin and a large blunt spine at the middle of the palmate margin and with with a group of long setae at the base of the dactylus (Fig. 3G). Gnathopods II with much weaker, heavily setose subrectangular elongated propodus with 4 transverse rows of long setae on the posterior edge (Fig. 3H). Pereopods short, with strong spines and few setae, coxal plates short, rounded, with very short setae on the posterior edge. Basipodite of pereopod VII with a triangle lobe tempering distally into a very short triangle protrusion not reaching the distal end of the basipodite (Fig. 3I). Posterior edge with 5-6 setae one of which, near the distant end, longer than others. Anterior margin with 3 spines, the one on distal-anterior corner of the basipodite stronger and longer than others. Pleopods of typical gammarid morphology, with 2 small (50 microns) retinacles on the basal article, with convex side smooth and 4–5 hooks on the concave side. Uropodes I and II with spines. Uropod III short, carrying numerous simple setae in bundles and strong spines on both sides of the outer ramus, which is twice as long as the peduncle. Peduncle with 1 weak and 3 strong spines, that reach beyond the tip of the inner ramus, which is short, triangle, ¼ as long as the outer ramus and caries only 4 long terminal setae. (Fig. 3J). Telson cleft to the base, carries 1 spine and 5 long setae on each branch (Fig. 3K). Remarks: Molecular phylogeny places this species within the paraphyletic genus Eulimnogammarus, (Fig. 4 below). Uropod III structure similar to that of E. viridiformes, E. lividus and E. cyanoides, but differs from these species by smaller body size, red coloration, much shorter antennae and lack of calceoli, and only one pair of spines only on the last 2 segments of urosome. Differs from E. obsoletus, E. exiguus and E. viridulus by the lack of distally protruding distant-posterior corner of posterior lobe on basipodite of pereopod VII and much denser setation of outer ramus of uropod III; from E. exiguus, to which it is probably closely related, also by much denser setation of antenna II, shorter inner ramus of uropod III and by presence of strong spines on peduncle of uropod III and on telson. Differs from all other Eulimnogammarus spp. except the previous species by having a 1-articulate accessory flagellum in at least some adults. This species is different from the previous one by very strong gnathopods, inner branch of uropod III shorter than 1/4 of the outer branch, dense setation on antennae II and uropod III and a nearly absent distal lobe on pereopod VII basipodite. The two species are remarkably similar in their red coloration when live, a typical homoplasy common among Baikal amphipods.

PouV and SoxB1 family transcription factors (TFs) have emerged as master regulators of cell fate transitions. To investigate the genetic interactions between Pou5f3 and Sox19b in zebrafish embryos passing through Zygotic Genome Activation (ZGA), we combined time-resolved mutant transcription analysis using the novel tool RNA-sense, chromatin state and phenotypic assays. We distinguish four types of embryonic enhancers, differentially regulated by the two TFs. Pou5f3 is critical for activation of enhancer types 1 and 2, which are responsible for transcription of genes involved in gastrulation and ventral genes. Pou5f3 or Sox19b prevent premature activation of type 3 and 4 enhancers, which are responsible for transcription of organogenesis regulators, differentiation factors and dorsal genes. We also show that the balance between Sox19b and Pou5f3 is important for bulk ZGA timing. Our results uncover how independent activities of maternal Pou5f3 and Sox19b add up or antagonize to determine the early gene expression repertoire. Bullet points Pou5f3 and Sox19b bind independently to DNA Disbalance between maternal Pou5f3 and Sox19b delays ZGA Pou5f3 suppresses premature transcription of neural patterning genes, activated by SoxB1 factors Pou5f3 and Sox19b synergistically suppress premature transcription of a wide range of differentiation genes Pou5f3 and Sox19b restrict the dorsal organizer

Gene expression responds to the environment, and can also evolve rapidly in response to altered selection regimes. Little is known, however, about the extent to which evolutionary adaptation to a particular type of stress involves changes in the within-generation (“plastic”) responses of gene expression to the stress. We used microarrays to quantify gene expression plasticity in response to ethanol in laboratory populations of Drosophila melanogaster differing in their history of ethanol exposure. Two populations (“R” populations) were maintained on regular medium, two (“E”) were maintained on medium supplemented with ethanol, and two (“M”) were maintained in a mixed regime in which half of the population was reared on one medium type, and half on the other, each generation. After more than 300 generations, embryos from each population were collected and exposed to either ethanol or water as a control, and RNA was extracted from the larvae shortly after hatching. Nearly 2000 transcripts showed significant within-generation responses to ethanol exposure. Evolutionary history also affected gene expression: the E and M populations were largely indistinguishable in expression, but differed significantly in expression from the R populations for over 100 transcripts, the majority of which did not show plastic responses. Notably, in no case was the interaction between selection regime and ethanol exposure significant after controlling for multiple comparisons, indicating that adaptation to ethanol in the E and M populations did not involve substantial changes in gene expression plasticity. The results give evidence that expression plasticity evolves considerably more slowly than mean expression.