We have identified benthic recruitment habitats and nursery grounds of the American lobster Homarus americanus Milne Edwards in the coastal Gulf of Maine, USA, by systematically censusing subtidal sediment, cobble, and ledge substrata. We distinguish lobsters between settlement size (5 mm carapace length (CL)) to ca 40 mm CL as the 'early benthic phase' (EBP) because they are ecologically and behaviorally distinct from larger lobsters EBP lobsters are cryptic and apparently restricted to shelter-providing habitats (primarily cobble substratum) in coastal Gulf of Maine. In these habitats we found average population densities of EBP lobsters as high as 6.9 m-2 EBP lobsters were virtually absent from ledge and sedimentary substrata devoid of vegetation although larger lobsters are commonly found there. It is possible that the requirement for shelter-providing substrata by this life phase creates a natural demographic 'bottleneck' to benthic recruitment for the species. Prime cobble recruitment habitat is relatively rare and comprises ca 11 % of the 60.2 km of shoreline at our study area in midcoast Maine. If this low availability of cobble exists throughout the Gulf of Maine, as other studies indicate, it could limit lobster production potential. We verified the geographic extent of recruitment to cobble habitats censused in 3 of 4 regions spanning ca 300 km of the coastal Gulf of Maine (from Nahant, Massachusetts to Swans Island, Maine). Early benthic phase lobsters were absent from cobble censused in the northeastern extreme of our survey (Swans Island). This pattern is consistent with earlier speculation that relatively cool water temperatures may limit larval settlement in this region.

/pdf/recruitment-habitats-and-nursery-grounds-of-the-american-2fdkvf4jbl.pdf

Recruitment Habitats and Nursery Grounds of the American Lobster Homarus Americanus: A Demographic Bottleneck?

Habitat restrictions in early benthic life: experiments on habitat selection and in situ predation with the American lobster

The question of whether there is a fundamental discontinuity between humans and other primates is discussed in relation to the predominantly human pattern of right-handedness and the left-cerebral representation of language. Both phenomena may go back at least to Homo habilis, 2-3 million years ago. However, a distinctively human mode of cognitive representation may not have emerged until later, beginning with H. erectus and the Acheulean tool culture about 1.5 million years ago and culminating with H. sapiens sapiens and rapid, flexible speech in the last 200,000 years. It is suggested that this mode is characterized by generativity, with multipart representations formed from elementary canonical parts (e.g., phonemes in speech, geons in visual perception). Generativity may be uniquely human and associated with the left-cerebral hemisphere. An alternative, analogue mode of representation, shared with other species, is associated with the right hemisphere in humans.

Laterality and human evolution.

Behavioral changes in fighting and the devel- opment of dominance relationships were analyzed in groups of juvenile crayfish ( Astacus astacus) using quantitative behavioral techniques. When individuals were placed into an aquarium, the number of agonistic challenges, their mean duration, and maximum intensity reached were high initially but then decreased steadily as the hierarchy developed. In all groups, linear hierarchies emerged which became increasingly stable over time. Winning influenced subsequent fighting behavior on two distinct time scales. In the short term, recent winners be- came progressively less likely to retreat. Second, indi- viduals occupying dominant positions for days became increasingly likely to escalate to higher intensities early in the encounter. Both effects biased the outcome of fu- ture interactions such that winning enhanced further suc- cess and losing decreased an individual's subsequent chances for dominance.

The formation and maintenance of crayfish hierarchies: behavioral and self-structuring properties

Chapter 4 – Postlarval, Juvenile, Adolescent, and Adult Ecology

The changes in relative efficacy of two incompatible behaviors was investigated during growth of the lobster, Homarus americanus. In larval and early juvenile stages, physiological and morphological factors favor use of the escape response over defensive behavior. In large animals, defensive behavior is preferred almost exclusively to escape behavior unless the claws are lost. The interaction of escape and defensive behavior is modified by neural and morphological factors, which are dependent on the stage in the life cycle of the organism.

https://science.sciencemag.org/content/sci/197/4304/682.full.pdf

Developmental neuroethology: changes in escape and defensive behavior during growth of the lobster.

1. The closer muscles of the dimorphic claws (chelipeds) were studied for the presence and location of fast and slow muscle fibers.2. Cutter claws were composed of about 60-70% short sarcomere ( 6 µm) slow and intermediate (4-6 µm) fibers.3. Crusher claws were composed of a uniform population of long sarcomere (6-13 µm) slow and intermediate (4-6 µm) fibers.4. There was a regional distribution of fibers in the cutter claw. Ventral fibers were predominantly slow. Dorsal fibers and central medial fibers were fast. Proximal and distal fibers in the medial section were usually mixed.5. The regional distribution of cutter fibers correlates with previous physiological studies on the distribution of the fast and slow motor axons to these muscle fibers.

Development of the dimorphic claw closer muscles of the lobster homarus americanus: i. regional distribution of muscle fiber types in adults

Like the chelipeds, the claw closer muscles of the adult lobster are asymmetric (dipmorphic). In the crusher claw the closer muscle is composed entirely of slow fibers, and in the cutter claw it has 65 to 75 percent fast fibers and 25 to 35 percent slow fibers. While claw placement in the adult is essentially random, it can be demonstrated in two ways that the muscle fiber properties are not genetically fixed: (i) if one claw is removed in the fourth and early fifth stages, the remaining closer muscle develops all slow muscle fibers, and (ii) if the animals are raised in smooth-bottomed containers, both claws can become cutter types, having closer muscles with more than 50 percent fast fibers. Thus, as in vertebrate skeletal muscle, the properties of lobster closer muscle fibers can be transformed by various experimental manipulations.

https://science.sciencemag.org/content/sci/201/4360/1037.full.pdf

Experimental transformation of muscle fiber properties in lobster

This study incorporates contractile, structural (sarcomere length), histochemical (myofibrillar ATPase and NADH diaphorase), and physiological (fast and slow axon innervation) parameters to define fiber types in lobster muscle. Single fibers were examined in the closer muscle of adult cutter and crusher claws and of developing larval claws of the lobster Homarus americanus. Fibers with short sarcomeres ( 6 μm) had rise times of 90–800 msec for reaching maximum tension, which either was subsequently held at this level or continued to increase. The contractile properties and sarcomere length of single fibers were correlated with their enzymatic properties such that fast-contracting, short-sarcomere fibers had high myofibrillar ATPase activity and low oxidative capacity compared to their slow-contracting, long-sarcomere counterparts. The slow fibers were also further differentiated into subcategories based on contractile and histochemical properties. Fibers with the fastest rise times tended to be innervated primarily by the fast axon, and those with the slowest rise times were supplied solely by the slow axon. The organization of the massive closer muscle into discrete bundles in which fibers have uniform contractile, structural, and physiological properties leads to functional subdivision within the muscle. The contractile properties of developing fibers were similar to the adult except that larval fibers did not possess very slow rise times.

Contractile responses of single fibers in lobster claw closer muscles: correlation with structure, histochemistry, and innervation

1. 1. Relationships between motor innervation and muscle fibre type were examined in the closer muscle of the claws of the lobster Homarus americanus . The dimorphic claws of the adult-the cutter and crusher-were compared with the claws of the juvenile (stages 4–6) when differentiation takes place. The muscle is known to receive a fast and a slow motor axon. Previous findings have shown that the crusher contains mostly slow fibres; the cutter and juvenile claws have both fast and slow fibres.

2. 2. In the adult, the majority of fibres in the crusher received fast and slow axons; in the cutter most fibres received the fast axon. Fast fibres in the cutter claw were innervated by the fast axon, alone or with the slow axon. Slow fibres in both claws could receive the slow axon only, or both axons. Some slow fibres in the crusher claw were innervated primarily or solely by the fast axon.

3. 3. In the juvenile, most fibres in each claw were innervated by both axons. The juvenile synapses were immature; postsynaptic potentials fluctuated greatly with frequent failures. The homologous fast axons in these claws formed fatigue-resistant synapses.

4. 4. In both adult and juvenile, regardless of fibre type, fast axon synapses had poor facilitation; slow axon synapses had moderate-to-high facilitation.

Note:

Walter J. Costello

Papers

Developmental neuroethology: changes in escape and defensive behavior during growth of the lobster.

Development of the dimorphic claw closer muscles of the lobster homarus americanus: i. regional distribution of muscle fiber types in adults

Experimental transformation of muscle fiber properties in lobster

Contractile responses of single fibers in lobster claw closer muscles: correlation with structure, histochemistry, and innervation

Innervation Patterns of Fast and Slow Motor Neurones During Development of a Lobster Neuromuscular System