Limitations of feed-fed LMB may not be just a function of learning curve. The physiology / morphology may need to change as well. Latter may take more than a few weeks..
What are your observations as to morphology?
Should be easy to find publications supporting morphological changes of sunfish as a function of prey type. From what I have seen, it is likely the changes to LMB are likely to be just as pronounced.
I know of one on OSS. I haven't read it but had assumed these morphological changes occur over a few generations. I suppose also that offspring of varying morphology are always in the population, those with morphology best suited for the most abundant prey have more reproductive success and quickly dominate.
Nobody has mentioned the impact of artificial selection at hatcheries with respect to feed training. At least some hatcheries, perhaps most by now, feed brooders prepared feed.
While epigenetic effects would likely subside after a generation or two, one has to wonder what they might be.
Very interesting topic and we have discussed it in prior PB articles. Bob was doing an article that several of us provided info on the topic for but not sure he has used the article yet. Here is a bit on the topic wrt lepomis sunfish. Keep in mind that all my comments in this thread are short term effects on LMB stocking ( a few mths but less than a year).
In these articles plasticity = adaptive behavior (adaptation) = phenotypic plasticity which can lead to morphological changes .
The Effect of Vegetation Density on Juvenile Bluegill Diet and Growth in the Journal of Freshwater Ecology 2012, 1–11 by Daniel E. Shoup , Michael A. Nannini & David H. Wahl discuss a number of their thoughts which are set out below.
At the start the authors noted that the role of vegetation density and its influence on juvenile bluegill diet and growth remains unclear. Even after the many studies that exist. They acknowledge much disagreement in the literature about how vegetation density affects foraging results and thus growth of juvenile bluegill. Several studies have found reduced foraging return for bluegill when they forage in structurally complex habitats, whereas others have found that bluegill growth was unaffected or even increased when foraging in complex environments. However these studies were with predators present. That is not the case when a typical bluegill or other forage base is first started in a new or renovated pond without predators.
In the Shoup et al study eight experimental 0.4-ha ponds (one acre with a mean depth of 1m) were used to evaluate the effects of habitat complexity on growth of small bluegill. Each pond was stocked with 15 kg of young-of-year bluegills (30–50 mm total length, approximately 20,000 fish per pond) to produce a realistic density for small ponds. The ponds contained varying amounts of vegetation (plants) and no predators.
The result was - by the end of the experiment, bluegill from the low vegetation treatment ponds were significantly longer – twenty (20%) percent than bluegill from the high vegetation treatment ponds. These results suggest that bluegill chose to forage in a vegetated habitat even in the absence of predation risk, resulting in reduced growth. The question is why and what caused the bluegill to stay and forage in the plants even when that was not optimum for growth and energy usage (energetics).
Because piscivorous fish were not present in the study ponds used by Sloup et al, it was surprising that bluegill foraged so heavily in the vegetated habitat. Either bluegill cannot accurately assess predation risk or some other mechanism causes bluegill to forage in vegetated habitat. The propensity of bluegill to forage in vegetated habitat could be genetically linked or related to phenotype . In both cases, fish would not be expected to alter their habitat use in response to the absence of predators over short time scales. Bluegill may also select habitat due to temperature preference rather than foraging return highlighting the potential for mechanisms other than predation risk.
The authors’ bottom line - additional research is needed to determine the pervasiveness of these behaviors and the underlying mechanisms.
One area I wish the study would have addressed in more detail is phenotypic plasticity. That is the ability of an individual or population to change due to environmental influences. Can environmental conditions during early development shape individuals’ phenotypes so they become more adaptive to the conditions they encounter? Were the long bluegill that fed in open water that way because longer fish can swim better in open water and were the shorter bluegill that way because being short allows them to maneuver around the weeds better? Plasticity has been shown to effect sunfish (Lepomis) shape, feeding and behavior in some cases.
Genetic relationships among pumpkinseed
(Lepomis gibbosus) ecomorphs in freshwater
reservoirs of Portugal
Morphological divergence in the form of trophic or
habitat polymorphism has been noted in a number of
freshwater species and occurs most often as a result of
low interspecific competition among cohabiting species
and high intraspecific competition within individuals
of the same species (Smith & Sku´ lason 1996).
The time span over which a species diverges into
distinct ecomorphs can vary, however, making it hard
to interpret if the differences have arisen as a result of
sympatry (i.e., within the same geographic range) or
had evolved in allopatry (in different geographical
locations) prior to secondary contact (Rundle &
Schluter 2004). A further complication is that morphological
diversification can also occur rapidly
among co-occurring conspecifics as a result of phenotypic
plasticity and ecological opportunity (Sku´ lason
& Smith 1995). This response is particularly
common for species in deglaciated environments and
in species-poor communities with abundant and
unexploited resources (Smith & Sku´ lason 1996), but
is also a characteristic of expanding and invasive
species (Yonekura et al. 2007; Pilger et al. 2008).
Therefore, introduced species provide good opportunities
to study the onset of contemporary evolution via
means of such rapid diversification (Stockwell et al.
As a group, Centrarchidae have been highly
successful in adapting to changing environments,
showing a high degree of phenotypic polymorphism
in both their native and introduced ranges (Robinson
et al. 1993; Hegrenes 2001; Brinsmead & Fox 2002;
Gillespie & Fox 2003; Yonekura et al. 2007; Pilger
et al. 2008). Introduced bluegill (Lepomis macrochirus)
populations in Japan are extremely efficient in
exploiting resources in both littoral and pelagic
habitats of lakes and reservoirs (Yonekura et al.
Ecology of Freshwater Fish 2011
Printed in Malaysia Ć All rights reserved
_ 2011 John Wiley & Sons A/S
Bhagat Y, Wilson CC, Fox MG, Ferreira MT. Genetic relationships among
pumpkinseed (Lepomis gibbosus) ecomorphs in freshwater reservoirs of
Ecology of Freshwater Fish 2011. _ 2011 John Wiley & Sons A⁄ S
Abstract – High levels of morphological differentiation have been found
among pumpkinseeds (Lepomis gibbosus) occupying four habitat types in
Portuguese reservoirs. To investigate the underlying mechanism behind the
phenotypic differentiation among ecomorphs, we used six microsatellite
markers to assess patterns of genetic differentiation among and within eight
naturalised reservoir populations. Greater genetic differentiation was seen
among reservoir populations than within reservoirs (FST > 0.041,
P < 0.002). structure analysis revealed the presence of two distinct
genetic groups among the set of eight reservoir populations. However, an
analysis of co-occurring forms that were identified a priori by their
respective habitats was consistent with a single panmictic group,
suggesting that morphological differentiation has arisen in sympatry (i.e.,
within a reservoir, postintroduction). The observed relationships within and
among reservoir populations, combined with the timeframe of ecomorph
divergence, suggest the strong likelihood of phenotypic plasticity as the
underlying mechanism of diversification in the introduced pumpkinseed.